Opium poppy seeds are legal, so that's kinda better than a "substitute." Also you can pick up the plants from garden stores (sometimes they even sell the flowers flattened and dry) so you can make opium tea.

Also, any mescaline-containing cactus you can get hold of would be legal and worth your while. Again, garden stores might have some San Pedroes.

I hear damiana is actually a pretty impressive high if its done right, so maybe you already have one good alternative. But don't ask me how to "do it right," I'd have to ask my friend.

I guess what I'd personally recommend is

LSA
Opium seeds
San Pedro cactus
Salvia

Also 2C-I (everybody knows the one solid research chem site for this) if you're not shy about white powders