There was no BK37 on the Hs129... They started testing and stopped right away. They shifted tracks entirely away from that. It wasn't rare, it was downright nonexistent. The Hs129's main claim to fame was the Mk101 and Mk103 guns. The majority of them that carried gunpods used these guns. The problem is that by even early 1943 they were having problems punching through Soviet armor. They were only 30mm rounds.
The 75mm was also rather rare, but actually used. 25 were made starting in June 1944 and ending in Sept 1944. That was when they shut down production.
So if you want a Hs129 representative of actual WW2 capabilities, it will have a 30mm gunpod or external bombs/rockets. In short, it was obsolete before 1943 came around, and Fw190Fs and obsolete Ju87Gs were much more capable of killing tanks. An interesting addition if ever added, but useless in almost every way related to Aces High MA play.
P.S. I think you should stop wishing for the Hs129 and just wish for the Ju87G. It had more ammo, better performance, and 2x the hitting power (twice the guns).