The HM fly is found west of celadon city there is a tree you can Cut down using the the HM Cut do so then go more west until you enter a big building keep going until you find a house go in and talk to the girl inside she will give you the HM Fly.
Fly is an HM and therefore it can only be taught to Pokemon. No wild Pokemon will know Fly ahead of time.
On route 16.
No, Butterfree cannot learn Fly.
Piplup does not exist in Pokemon LeafGreen or FireRed.
No, you cannot find cyndaquil in LeafGreen.
you should go to gamestop
chach a rear leaf Pokemon that fly
LeafGreen version does not have Growlithe.
The HM's that are in leafgreen are: Cut, Fly, Surf, Strength, Flash, Rock Smash, Waterfall.
In the grass...
threre isn't one sry but you can get the fly tipes like zapidos and legendary Pokemon! >)
You cannot catch houndour in Pokemon leafgreen either get one from Pokemon emerald or Pokemon colosseum.