You can't without trading from other games or cheats.
The mall has some of the TMs, but you have to find most of them youeself.
Yes, all the TMs that were in Pokemon X and Y will be available as TMs in Pokemon Omega Ruby and Alpha Sapphire.
You cannot get another copy of the TM Dig in Pokemon Emerald. All TMs are a onetime use item and often have only one obtainable copy in each game. This was however changed in Pokemon X and Y so that TMs could be used multiple times like HMs.
at the lilycove city department store, on the floor that sells TMs
no
You can't. In Ruby, Sapphire, and Emerald you can only buy items, TMs and dolls.
you use action replay
cheat
there are 50 TMs in Pokemon gold, and 7 HMs
get all the Pokemon in the emerald dex
the pokemart part of a Pokemon center you can sell HMS or tms you don't need TMs cannot be sold in Black and White.
mew can learn all tms and so can mew2