I re-read this thread a few days ago and it got me thinking. If one wanted to build a sort-of repro and wanted to avoid the AOW aspect of a gripless pistol, you could use some KelTec parts. They make extended magazines (9 or 10 rounds I believe) for the P-32 and the P3AT pocket pistols that extend the grip from stubby to full grips. The magazine wells are not actually on the receivers of those guns. The 'receiver' is a milled aluminum block thingy that sits inside the plastic outer shell. That shell is available without transferring as a firearm. You can get it with the mag release and have brand new, modern magazines for your WelRod. Just trim the plastic down to wherever you need it, leaving a stubby little grip on the bottom of the gun that becomes a full length grip with the mag installed.
I am not US resident, so I do not carry about AOW regulations. For the same reason it would be quite difficult to get any KelTec parts.
But I was thinking in the similar direction, I plan to use mags from russian Izh-71, what I can get. This is .380 ACP pistol. Suppressor is also going to be modern. The rest is just like in the original Welrod.
Somewhere on this forum I saw a topic about building the modern version of Welrod using parts of modern pistols, like SIG-Sauer P250.