I haven't made any more progress but the obvious did dawn on me. If I don't a suitable plastic body for my Lost in Space Robot, I can always make the whole thing from foam. That would probably look better but it's not the point of my build. And turning foam is messy. If I thought I could find a plastic part for the treads I'd use it too.
Fellow blogger KenKzak found another scale subject that is basically a nose cone with fins. It looks cool but I won't steal his thunder. You will have to wait for the build posts on ZZakk's Lab.
After hearing about them on one of the forums, I ordered a few motors from Winkies. Their prices aren't quite as low as Hobbylinc, but close. And it looked like the motors I wanted were available. I ordered on a Thursday and got a call Sunday. About half my order was "not available form the manufacturer." So, the good news is that someone acted on the order quickly and the bad is that their website doesn't reflect their stock. So, I canceled what wasn't available and proceeded with the rest. A bit over a week later, the order status finally indicated it had shipped and USPS says it's in route. Looks like it will be about 2 weeks from start to finish. Since they actually answer the phone, it's probably a good idea to call in advance. Assume the order is correct unless I bitch about it.