Choate makes a stock that's both folding and collapsible. I have one one on a tactical conversion fo a 870 I'm working on now. The recoil pad isn't very thick though. I'll post some pics when it's done. Midway sells them.
Don't like the anti shock ones shot a friends a couple times felt like the recoil punched me in the face instead of the shoulder. Personally I'd rather keep the recoil it's a 12g reminds ya every time ya pull the trigger.