After a good few years of debate, a decent alternative drive belt has been found by forum member Steph99 (well done on finding the missing piece of thje jigsaw).
The replacement is a belt for a Malaguti madison 125 1999-2005
Available from www.chinesemotorcyclepartsonline.co.uk
Drive Belt 22-30-828 V-Belt Malaguti Madison 125 99-05, price £15.37 free delivery
One thing to note though; While it works in a static test, as yet it has never been road tested (be warned). It has been noticed that the belt rides a little high in the front pully but this should be corrected by simple shims between the reaction plate and the outer pully.