Prop rings and jewelry

[MrBackpack]

lets just say that I'm trying to make a prop ring that has an unusual gem set into the face, like a more book accurate LotR ring, Captain Planet rings or even a Green Lantern ring.

Where would I get someone to make an oddly shaped gem that would be set into the ring? I'm not talking about a precious gem or anything, but color glass or something similar that I could have set into a silver ring.

Thanks and sorry if this is in the wrong place.