Ahhh, truly a unique beast. That is based on the EC Rookie and it appears to be a motor based on the 80cc Trials bike. Have you tried GoFasters just for S41ts & Giggles? They have a direct line back to the factory in Spain and usually enjoy a challenge.
Looking at the factory site, it appears I'm all wet on the pre-05 SM 50's. The SM has always been in the Rookie frame, not the mini frame.
Good luck.
This is the bike I'm thinking about
:
A considerably different bike.