Helium-3 (H3 is tritium, and to my knowledge there is no tritium in significant quanities) is present on the moon due to constant bombardment by the solar wind. It is retained in the regolith itself, although it (being essentially inert) isn't chemically bonded to it (think of some materials, such as ilmenite, a mineral composed of iron, titanium, and oxygen, as a "sponge" for it).
Mining it is almost trivial. All you have to do is find the areas with the densest concentration (for example, maria on the far side), pick up the dust, and heat it. Due to the way it got there, the richest deposits are all on the surface. It's almost as if all the gold in a gold mine were in the form of nuggets you could pick up as you walked around it.