If you have access to a lathe and a hunk o' 3/4 aluminium round bar then you can make your own assuming you can use the lathe OK.
Just make up a solid stub that has the same shape as the stub with the 2 Orings on the VA that goes into the main body. But don't drill out the holes just yet. Leave it so there's about 3/8 inch of bar sticking out. Drill and tap the hole for the retaining screw being careful to go only just deep enough to hold the screw. Then drill in with the Q drill but stop short of the retainer screw drilling by about 3/32 inch to 1/8 inch. Use a 1/8 NPT tap to thread this hole. Drilling in about 1/8 inch with a drill bit that is a 1/64 oversize will really help reduce the amount of metal the tapered form of the NPT tap has to remove. The hole for the adapter will need to be a touch low of center. Then from the back you'll need to drill in to hit the back of the Q hole to pass the CO2 through to the valve chamber. But you need to do this without hitting the hole for the retaining screw.