You can fit 9 rounds of 45 GAP to a Glock 38 magazine like the one I am selling on the link. (Extended Magazine as a backup)
I know the G38 magazine specs. says it can fit 8 rounds, but it will fit 9 rounds using a magazine loader by Glock. 9+1 if you load one in the chamber.
The Glock 37 magazine can fit 10 rounds, but it will not be flushed or no magazine spacer available.