I would use someone that does online auctions. You could supply the info on the tractors and they could take detailed pictures. Like the others have said the parts, I would put on EBay.

I'd be concerned that with 150 Cubs, even bringing in the right crowd for an auction on site won't get the best prices for your stuff. You'd have to get a whole lot of people each wanting at least one or two Cubs; otherwise, the most desirable 10-20 will bring good money and the other 100+ bringing very little.
Why not list quite a few on here, craigslist, etc for the prices you want just to test the waters? I know it's a lot to deal with each mower separately but probably get better money.