i bought a new oil cap, $4.95 at autozone, but i needed something temporarily.
as far as losing it, well i dont think i actually lost it, its probably in the shop... somewhere... ill find it in a few years im sure.
I thought about duct tape and electrical tape, my fear was that it might melt and be a big mess. which is why iused HVac tape. It worked quite well, i tapped a hole in the top so that any moisture would hopefully evaporate out.