[Wiking]

Hard mode: Only vehicles that the enemy abandons on the battlefield, and are not destroyed by the end of the fight. Keep a running tally of the make, model and number of each.

Somewhat sane mode: Maybe go off of historical numbers of captured vehicles or what was used in the theater of operations? Or maybe construct a table of various tank and gun type that are possibly captured and do a random roll? I'd still try to break it down into heavy/medium/light/tankette though, so you don't have a KV-1 leading BT-7's...