I grew up with them, still have the 175 trials bike that I built a frame for in my teens for classic trials.
Depending on what engine parts you need I may be able to help, the engine is the same for the 175s apart from crank, barrel,head & centre cases so you can use the gearbox, clutch etc if needed.
The 125 head can be used on a 175 with no modifications to increase compression, as standard they always had quite a bit more power than BSA bantams
Jawamarkt
http://www.jawamarkt.cz/en/Points are 2euro, Vape electronic ignition is 162-166euro depending on 6 or 12 volts, looks like they have looms as well
Jawashop
http://www.jawashop.com/Points $2.69us
My memory is that the charging system esp. regulator isn't great, I know a guy over here who runs the Vape system in his 350 twin & he loves it