eBay 
I haven't tried one yet but If you want to stick with the original type this may well be the closest. 
 It will need re-jetting but the original jets should fit or new ones easily got off Dave Silver, Gordon F. etc 
This chap has several in stock and seem a good price (?)  
I paid a bit more for mine and from a different seller, but they look the same. I am just waiting for new jets before I try it on my TLR250 
It has the original bass floats like the TLR's, SL125, etc. 
Cheers,  
Ace