Hi Steve,
Some are SMS, or ZX graphics only. Some are for portable graphics of various types 2D, 3D, turtle graphics, etc.
I've built a few at different times for the Z88 emulator and ZX / ZXN machines, and they're pretty good.
But that's probably not going to be too useful as SMS is quite specific in its banking etc.
IDK how it works.
Again mainly ZX related, but they might work for you too.
Hope that helps.
Phillip