I know that in normal conditions, a Golbat will not evolve into a Crobat until the National Pokedex is recieved. But can it be obtained via other methods like trading?
If you have two GBAs and two copies of either Fire Red or Leaf Green then it's possible so long as one of those copies has the National Dex.
Trade the Crobat from the copy with the National Dex to the game without the National Dex. Simple!
I remember seeing this on a Youtube video so I'll try and find that and link it in here.