1. Scratch-built from paper. The only problem is the wheels of the track. On the other hand, I can try my own designs. For instance, 'tis vehicle below.
(clearly a sketch, just something I made up now)
Another solution is to use some old toys (from those cheap 54mm 'made in China' sets) for conversions as the vehicles are significantly smaller scale than the figures themselves.
2. Conversions from existing vehicles. I've had the idea in mind that a KV-2 turret on anything (presumably an AFV with an uncomfortable height on battlefield, just as they were originally) would look rather odd (thus totally acceptable) for the task.
Staying to the topic, the early USSR designs (T-35, T-28) are kinda similar in this way, at least they look weird. Could also manage to get WWI vehicles (Airfix Landship Mark I etc.)