If you go to the local parts stores they typically sell them individually behind the counter or you can go to Rockauto and do the same. Rockauto has a better selection though. Heck you buy a whole new set of Amazon for 20-30 bucks. It will cost more than that for an individual on shipping these days.
Went down to dealer today and they actually had 4 different lug-nuts for early RAV4 (1996). Three of them were acorn-type for steel-wheels. Last one part# 90942-01058 was for mag-wheels with flat outer-end instead of domed. They looked up MKII Supra lug-nut, part# 90942-01050 (also used on Cressida and rear of MR2). They wanted $14+tax for it! Wow!!! But if I order from their on-line site, I get $4 discount, but will have to pay shipping.
Anyway, I found following are similar enough to use: