Offhand, I'd put a "want-to-buy" thread up on here and a few other boards. For some unknown reason, people have been pretty free with their money and spend a lot of Quatloos on their "almost" MP5 clones and quite a few have gone in the opposite direction. There should be plenty of "take-off" fixed stocks for sale
The .22LR HK/Umarex MP5s come with the collapsible stock, so there aren't likely to be too many "take-offs" around unless someone bought the aftermarket fixed stock to replace the one that came with it and then didn't like it. Real HK94/MP5 stocks won't fit on the Umarex guns, so you can't use a "take-off" from a full caliber gun. HKParts has the Umarex fixed stock, last I looked.
Haven't seen any used either for the Umarex. Currently it looks like the above link from CTD is about $20 less than others are charging. As noted the real HK94/MP5 stocks, nor the GSG, versions will work on the Umarex. The added length of pull on the A2 style is nice, plus no issues with the painting wearing as with opening/closing the A3 style that comes on the Umarex.
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