You can purchase Impact products from eBay, or Mitosal.com. I am not sure if any of the other mainstream RC tank vendors stock their products.

The tow pintle, cupola AA gun mount, and AA gun comes from Axels Modellbau. The manufacturer is Schumo-Kits.

The tow shackles are Aber products. I bought them from an eBay seller in Virginia.

The JagdPanther parts were graciously given to me by Dana Lowell while we were at Danville. He refused to take payment for it, so I owe him a beer. You can probably order the parts tree easily from your local hobby shop since you're in Japan.