That lever which locks the cylinder in place is the most poorly designed piece of shite I've seen. Like you said, it's a piece of pot metal with a piece of what should-be spring steel press fit to it. Every time you cock the hammer, it puts pressure on the steel piece and in turn on to the press fitting. It's almost designed to destroy itself eventually. I've tried to cut my own piece out of a square bit of metal, but it's just so damn small and oddly shaped.
I love my Tanaka revolvers but that part alone keeps me from using them more often. Boo-urns Boo-urns...
M
EDIT: Here's the closest I've come to finding a new one:
http://www.uncompany.com/pageproduct...sp?prodid=9927