I recently purchased a fobus holster for my tokyo marui Glock 17. I should of done a bit of research to find out that TM glocks measurements aren't identical to the actual gun, they're slightly bigger. Apparently this is to get around licensing? Weather or not that is true I found myself with a holster that was too small. I've drilled two of the rivets out and the gun slides in nicely and locks into place. I'll get some spacers from work next week, I just wanted to share this to anyone whose looking for a holster.
I've read somewhere that the holsters for G21 fit as it a high caliper gun so it's wider. Not tried it myself so best of luck!
The holster:
The gap needed for the gun to fit: