Seems to me that Ade V had some extra tanks from the last S-O-M that he purchased, but I think he's in Spain & not where the tanks are located. PM him, if he's unable to help I will most likely not use the one that came with my Omega 20/2, be forewarned that it has some rust in it (indian rust at that). I was going to put some Redcoat in it to seal the rust in & prevent the normal Roid leakage.
None of my tanks are "proper" CS tanks - with the exception of the one embossed with LISTER (which I assume is a "proper" tank of a small engine, like a "D" maybe). I'd suggest that the 3 I got probably originally belonged to cement mixers...
Anyway, once I've had a chance to look at them properly, I'll be able to tell if I've got any that don't leak...