Where can you buy ether or max ether in Pokemon fire red?

You can't buy them anywhere, I believe, however you can find them in item balls in the following areas:

Elixir (restores 10 PP to all moves) - Pokemon Tower/Power Plant/Six Island water path

Ether (restores 10 PP to one move) - Route 2/S.S. Anne/Celadon City/One Island Kindle Road

Max Elixer (restores all PP to all moves) - Berry Forest/Seven Island Sevault Canyon/Cerulean Cave

Max Ether (restores all PP to one move) - Rock Tunnel/Rocket Hideout/Berry Forest -- Valuable Hint: Get a Meowth or a Zigzagoon to pick them up for you in those places. He (or She) will pick the invisible ones as long as you don't make him hold something. Every time you move a considerable amount of steps s/he should be holding an item, so check on your Meowth/Zigzagoon often :)