Tom,
Good luck on your search. I tried to find one of these for about 3 months last year and couldn't even find a broken one! I ended up with an Electro-Harmonix Q-tron+, which is actually made by Mike Biegel, designer of the Mutron. You are probably familiar with the Qtron, but if not, try one out. I have been really happy with mine. I use it with my Tribute.