Fabricating the nuclear trigger, typically Po-210 and Berrylium, requires near constant, unlimited access to a working nuclear reactor. Po-210 has a half-life of a mere 140 days.
Plutonium is pyrophoric. Go look it up (if you're going to be posting about atomic bombs, then you need to know that word). You only work with Plutonium in very advanced clean room labs.
I have read a lot of what has been published about the early nuclear bombs of WW 2, and my understanding is that the U-235 or "cannonball" bomb didn't need the exotic trigger materials and was not a high tech design at all. It seems that the Navy weapons people charged with designing the "gun" worried about catching the "plug" if it went through the "doughnut" without going off. They were assured by Oppenheimer's people that there was nothing to worry about. It was only the plutonium implosion bomb design that got into exotic design problems because it required literally squeezing a solid metal sphere into a smaller volume in microseconds, something that had never been done.