Well, there are no Shroomish/Breloom in Fire Red/Leaf Green. Wild Parasect are found in the Safari Zone and in the Unknown Dungeon (The cave by Cerulean City where Mewtwo resides). Parasect in the Safari Zone won't help you teach your Smeargle Spore, but the ones in the Unknown Dungeon should know Spore, and considering that Parasect learns Spore at Level 27, their level will be high enough so that they should know Spore.