That's a rare one. Haven't seen one in a few years, and there's a bit of a story to that one. Local shop buys a parts box from some older former player. Shop owner calls me up and wants me to help sorting it all out. After digging through the whole thing we find one Typhoon (now mine, still needs a rebuild), a Mega Z clone (a Boxer I think), a complete VM-68, and yes, a double trouble trigger frame for it.
I babbled incoherently for about 10 minutes after pulling that out of the box. ("wow...it's...it's... no fricken way... wow... it's...") I quickly assemble the VM with the double trouble and we proceed to waste a LOT of CO2 around the shop. Don't know how players ever actually fed paint into that setup, there's no way a plain gravity feed would do it. Trigger pull is still VM stiff, so fatigue will still be a limiting factor over a long game.
Anywho I do a little internet bragging around the forums, mentioning the name of the shop (a little free advertising for my buddy). The next day my friend gets a call from someone who says their name is listed on the original patent for that trigger and even they didn't have a working example and would very much like to purchase it. The shop (being a business) gladly sold it to them at a price they both were happy with.
So one of the guys who invented the darn thing had trouble finding one. As for us mere mortals, well good luck.
Nunquam emere quid potes facere