Yeah, you can get them in G/S/C.
If you go see Bill's grandfather on the Cerulean Cape, he'll ask you to show him some pokemon, and if you bring him the right ones, he'll give you the stones. (Er... not at once of course, you'll have to show him the pokemon one by one)
And if you have crystal, some trainers that get your phone number call you sometimes and say that they've found something. If you go to the route they're on and talk to them, they'll give you a stone.
I can't quite remember all the phone numbers you need, but I do know that if you have School Boy Alan's and Lass Dana's, they give you fire and thunder stones.
