You might try rolling your own. Windworld.com offers films in lengths to do any sort of mounting. They have multiple sizes, so you can split or use a single strip. I bought some to test with but haven't gotten around to disassemble and rework my 12-string yet.
My plan was to affix them to the bridge underside and redo the bridge mount with inserts and machine screws so I can safely experiment. I'm using a Gotoh 12-string bridge from W on it, so this should work. The 2.5 inch single film should suffice and supposedly, they are durable enough to take the pressure. Whether this will work or not really needs testing. An alternative mounting suggested was extending the film out to one side of the bridge and isolate but attach the loose part to the body a bit with double sided sticky tape.
I should mention, they have preamps for them too, if you are going to try and merge with magnetics or plan to run normal stage length cables. I'm not starting with one, but will test it out first and drop two temporary female jacks out and mix separately till I figure out what works and what doesn't. It needs a preamp in any case with a cable run of over 4 feet.
