Tigerman, you have piqued my interest but I'm not sure I'd have anything off the top that would fit.
For a jagdpanzer would you be going all German or would other tank hunters be ok? I picked up a FineMolds Imperial Japanese Type 3 Ho-Ni tank destroyer last year that I thought about tossing into the SP Gun GB till I found out that the IJA only used the Ho-Ni in a direct fire role so it really didn't fit. I remember there was a tank hunter GB that ended about the time I joined the forum. I'd be happy to toss her in if ok, if not it's not a problem.
http://www.missing-lynx.com/gallery/axis/type3honi35sz_1.html
For a heavy GB I have a US M46 Patton if you'd be willing to streach the time frame to include the Korean War and a British Challenger (Second World War and Korea markings) but it's limited run and I'm a little afraid to tackle it.
No big deal either way, whatever you way you want to roll with it