Amanita Muscaria is found all over the place, but many subspecies, for example those in the Western Hemisphere, fail to produce the halucinogenic chemicals. Strength varies in the Eastern Hemisphere as well.
You can buy this fungus to grow in your flower garden if you wish.
If you read up on the way this particular mushroom is ingested, you'd soon discover that the active ingredient is NOT metabolized in the human (or reindeer) systems, but is excreted by the kidneys into the urine.
You would have also discovered that upon initial ingestion there is yet another substance in this mushroom that gives you stomach cramps and other uncomfortable symptoms.
Accordingly, you find a shaman or witch-doctor to eat the mushroom. Only he need suffer the cramps. Then you collect his urine and pass the bottle. Supposedly it is possible to run this material through the kidneys of 5 individuals before the concentration is too thin to give the desired effect.
Better yet is to feed your reindeer vast quantities of amanita muscaria. They love the stuff. Some sources say that reindeer are so addicted to this mushroom that should a Saami unloosen his trousers to urinate, reindeer will come running! (No doubt that's an apocryphal story about how to catch a wild reindeer). On the other hand, National Geographic has a film of reindeer eating absolutely huge quantities of this mushroom with tremendous gusto. Later they are shown urinating into buckets!
Add 2 and 2 together and you can see that the water in frozen urine is going to end up sublimating away leaving behind a yellow or brown powder just choc full of the active ingredients!
It is not to be believed that the Saami didn't happen upon such a process, particularly since this particular mushroom has it's peak growth period sometime in August. Whatever would the shaman do in the other 11 months if they didn't have a year round source?
In Ghengis Khan's day the Saami may well have had the best stash available, and they could produce it in large volume. There were no secrets from the Mongols.
I buy your description if you replace the Uralic speaking Saami by Paleosiberian speaking Koryak and related groups in Kamchatka
http://www.koryaks.net/. here is a link to a description of the distribution of Sami
http://www.linguistlist.org/issues/4/4-758.html and here is a description from 1730 about the use of urine
http://entheogen.netfirms.com/articles/articles/mushrooms_and_religion.html :
Despite the problem of identiy of Soma, the knowledge that A. muscaria contains psychoactive toxins has been known to Western cultures at least since 1730. Colonel Johann von Strahlenberg, a Swedish military officer, who was a prisoner of war in Siberia for twelve years reported on the use of A. muscaria as an inebriant by the primitive tribesmen in that area.
Throughout the history of the various tribes of Siberian mushroom users, there had been no other intoxicant other than A. muscaria until the Russians introduced alcohol. Thus, not all cultures developed the knowledge of fermentation. The mushrooms are dried in the sun and later ingested alone, or as an extract in water or reindeer milk. Few people know about how the mushrooms are treated after their collection, but it seems that one method of ingestion is well known because of the unusual means by which the psychoactive toxin are introduced into the body.
During the ceremonial use of the A. muscaria, a ritualistic practice of urine-drinking had developed because the tribesmen learned that the psychoactive toxins involved passed through the metabolic system unaltered. This practice allowed the toxin to be used over and over again by drinking the urine of someone who had consumed the mushroom or who had drunk the urine of someone who had consumed the mushroom. In this matter, the ecstasy of few mushrooms could be extended for several days.
An early account, in 1809, by Georg Langsdorf, on the practice of urine drinking, among the Koryak tribe of Siberia, described the reason for this practicve. He wrote: The Russians who trade with them [Koryak], carry thither a kind of mushrooms, called, in the Russian Tongue, Muchumor, which they exchange for squirrels, fox, ermin, sable and other furs: Those who are rich among them, lay up large provisions of these mushrooms, for the winter. When they make a feast, they pour water upon some of these mushrooms, and boil them. They then drink the liquor, which intoxicate them; the poorer sort, who cannot afford to lay in a store of these mushrooms, post themselves, on these occasions, round the huts of the rich, and watch the opportunity of the guests coming down to make water; and then hold a wooden bowl to receive the urine, which they drink off greedily, as having still some virtune of the mushroom in it, and by this way they also get drunk.
Although partially true, Langsdorf?s tale tells only half the story. Because the purpose of drinking the extract of the mushroom was for religious reasons, it is thought that the sharing of the shaman's own intoxicating body fluid with his fellow tribesmen, and theirs among themselves, served to show unification of the celebrants with one another as well as with the sacred mushroom. Recall also that A. muscaria contains muscarine, as well as other toxins that cause profuse sweating and twitching.
When drinking the urine of individuals, who had consumed the mushroom, apparently the muscarine and other toxins are metabolized and the urine drinker is spared the unpleasant side effects. Thus, there is a practical reason for drinking the intoxicating urine.