So far, I have had good luck with this. My collection now includes boron, fluorine (as calcium fluoride), sodium, aluminum, silicon, red phosphorus, sulfur, chlorine, manganese, iron, nickel, copper, zinc, gallium, arsenic, bromine, strontium, silver, cadmium, indium, antimony, iodine, barium, cerium, praseodymium, dysprosium, holmium, platinum, gold, mercury, thallium, bismuth, and americium (in smoke detectors). Potassium and uranium are on the way and should arrive soon.
Aside from the ones I mentioned earlier, sources include Metallium for most of them; a local rock shop for boron crystals and silicon; United Nuclear for potassium and uranium; and Home Depot for smoke detectors (americium). Unfortunately, United Nuclear ran out of thorium before I could get any, but I managed to get some of the last of their uranium. Thorium metal might be hard to get if United Nuclear doesn't get any more, but thorium ore is easy to get, so I'll have to be satisfied with that until something better shows up.
Regarding uranium, apparently the oxide can spall off and become airborne as it forms - considering that I don't want alpha-emitting dust in the air, it might be wise to store it in mineral oil. Has anyone else here had issues with uranium oxide formation? In a small sample, it's probably not a huge problem, but better safe than sorry.
I plan on getting pictures before long; when I do, I will post them.
Thanks for the suggestions in this thread - it has been helpful.
Heather