I have been told that the serial numbers are stamped, or cast, into the transmission case, near the top cover, on the right side, as you hold the handle bars. Below where the handle bar assembly is bolted on. You won't see the number when holding the handle-bars--it is down on the right side of the box!
As for the seals being available, they have been, but you should contact somebody in a mower repair shop, or tractor shop.
Somebody here can probably aid you, if you publish the model number.
Also, the common right side/left side instruction, is as you hold the handle bars, or the steering wheel of anything, be it a car, truck, tractor, or anything like that. Always! Not as you stand in front of the machine, and look at it! A lot of parts have been bought, or ordered mistakenly, because some folks didn't realize that fact. And, especially when ordering electrical parts. Suppliers won't usually take back anything electrical in nature, if ordered wrongly! HTH: RJ

Any good bearing supplier should be able to get you any bearing and seal you need. The seals should have numbers on them and they can be cross-referenced. As for the roll pin in the axle, drive it out with a punch. Usually they fall out and I put hose clamps around them and haven't had a problem since.

Yep, horses. Are the pins rusted tight to the axle? Time and penetrant are you best friends there...