I have replied to your email with the file we can provide. Please do not post the same message to our feedback form and the forum.
In case anyone else has the same question, we do not have the rights to the mini sumo chassis, so we cannot distribute it. We can provide the file for the small yellow chassis (https://www.pololu.com/lsrproj/lsrprj01/), but it’s not necessarily the best starting point. The only really valuable part is the t-shaped cutout for the GM7 gearbox, and getting consistent press fits is difficult.