Small Engine Troubleshooting Problems? Ask a Mechanic Now.
The gasket should be available from any good local Tecumseh dealer and it is also avaialble online. I've linked the part numbers to a source. I've also included the part number for the crankshaft seal, since it's a good idea to replace it at the same time.
Side Cover Gasket 37342
Crankshaft Seal 35319
I hope this is helpful.