In the T2k forum there recently was a post on the NATO rapid reaction force. They used a 105mm Pack howitzer until 1975.
OTO Melara Mod 56
The facts that they were retired at a perfect time for the project, and that they can be broken into 12 ~125kg parts makes them really promising as an option for my project.
The project just needs to buy them as scrap metal, perhaps manufacturing only the barrel (as I expect it would be tapped and replacements would be desired post oops).
I also had my project buy retired manufacturing equipment (as those jobs moved overseas) as scrap metal so that part of the cover story would match up nicely.