1979 Murray 11/36 Peerless Transaxle

TL;DR - Looking for gears/rebuild for Peerless 600 series transaxle.

Hello all! I am working on what I believe is 1979 Murray 11 hp 36 inch deck lawn tractor model 0-3667. So far I have got the old Briggs and Stratton 11 hp engine running nice and strong, rebuilt the steering, replaced the front tires, and replaced the seat. My next task is getting the mower to drive and stop. I was able to track down some brake pads which should be here today or tomorrow so hopefully with those and a bit of tinkering I can get the tractor to stop. However, after replacing the idler pullies and a new drive belt I am still only able to get the the Peerless Series 600 3 speed to shift into 3rd gear. When I was doing a fluid flush I could hear some rattling inside the case, so I am guessing there are a few teeth that are missing on the gears. I have done a ton of searching and am having no luck finding information or replacement gears for the series 600. I am not against full replacement; but don't want to spend a ton.

Does anyone have a lead on replacement gears for a Peerless 600 series 3 speed? Or maybe even a full transaxle replacement? Or is there a different transaxle out there that I can swap in and have a better chance of finding parts for?

Thanks