What makes you think you can not get parts ?
When Tecumseh went belly up Peerless split off.
Most parts are available.
I think the factory that makes parts is still running but they are no longer supplying boxes for new mowers.
I have no problems getting parts for them.
If the bits of the case that broke away are large most alloy welding shops will be able to put Humpty Dumpty back together again provided you clean all the grease out.
New cases are available but not cheap.
almost every mower repair shop will have racks full of old trannys .
Must be repair shop not glass front new mower shop, they send repairable mowers to scrap metal merchants to make yo buy a new mower , from them.
The best site for information is
http://peerlessgearboxspares.co.uk/part-lists-and-manuals/ as they list them by Peerless numbers
You can get the same information from
http://www.mymowerparts.com/pdf/Tecumseh-Peerless-Transmissions-Transaxles-Differentials-Gear-Boxs/ but they are listed by the peerless file numbers.