Interesting regarding the hidden rifles, old government buildings seem to be common, I have read of several similar situations, especially in more rural areas. Railyards were common too, so too old estates, though such places weren't suitable for long term hiding. I never read that the IAMCC searching civil institutions.. probably why they survived hidden so long. They were focused upon industrial concerns and military or former military structures. A few thousand men, inspectors being a small fraction of those present could never hope to search every home business or courthouse. Though there was no real reason anyway, they knew the Germans hid large numbers of rifles and equipment, Germany was awash in spies and informers (especially Prussia where the Prussian police routinely captured Reichsheer/volunteers hidden stores, - so it wasn't only the IAMCC after them...) but the central government knew the full scope (inventory) by 1926 for sure, Seeckt's replacement, General Heye informed the government of all efforts in this regard and the government took steps to stop Prussia from interfering (IAMCC was out the door by 1927).
Bavaria was always a hot spot anyway, I bet more exist in Bavaria than the rest combined, the nature of the region and rural environment (not to mention their close-up of what communism represents...) made it a prime hiding ground for illegal weapons.
Dietrich was a solid collector too, he was part of a email group a decade ago and had some really good observations, some of which I saved. Iknow CB was among that group, possibly PeterS and Bugan also, but I haven't heard of him in nearly a decade.