I sell a lot of vintage razors (as well as new safety razors, brushes, creams and soaps etc) via my web site - I think it breaks B&B rules to advertise it though. Anyway, it looks like there are plenty of these around for a good price.
Incidentally, tried the Twist this morning with my usual blade type (which I use in a Fat Boy and Merkur 1904) and I had a really uncomfortable shave - much like shaving with a really dull blade, not sure what happened - I'll try another blade in case the first was faulty - or put the same blade in the Fat Boy and try.
Pay close attention to your shave angle. The Slim Twist surely requires a different angle. Try holding the head on your arm and adjusting the angle until you see the proper contact of blade with skin. Remember and use that same angle on the face.