I contacted trialspartsusa/rising sun. Not sure if it was Jim I talked to. He didn't have much info and refereed me to trials training center in Tn......
Well, it was worth a shot.
There was some discussion and some pictures of GasGas 50cc bikes
in this thread.
http://www.gasgasrider.org/forum/showthread.php?t=2228&page=2
I think GasGas has used several different 50 and 65cc motors going back
to 2000 or so.
I know for sure that the crank case (bottom end) for the ~2002 era 50 and 70cc
motors were made by Franco Morini. As shown in the above thread.
Some of the 50cc motors were air cooled, as in the txt boy model. I think
they were made by Morinni.
I have found no confirmation, but, it is rumored that they also used the
Aprilia AM6 motor at some time.
From the above post. I am also looking for information on the GasGas 50cc
motor in my EC50SM. So far without much luck. I think Franco Morini is
out of business. Herdan has no parts for the Morini MC65 motor that is the
basis for the GG 50SM and 70TXT motor in my post. Also the importer
for Morini,
http://www.morinifrancousa.com/ , say they do not have parts
for the MC65 motor. Even though they list it on their web site.
If you already tried Treatland,
https://www.treatland.tv/ there is another
source you might try 1977 mopeds,
http://www.1977mopeds.com/
As a last resort start calling GasGas dealers,
http://www.gasgas.com/dealers.htm
Adrian and Mandy @ LewisSport have been helpful to me in the past.
Best of luck, Jeff