28539 for the clip and 28540 for the seal, both should still be available parts through certain vendors as they remained the same through many years although the sidecover itself was updated a few times over the years
If that engine was literally running without those items installed that's a bad thing. without the clip the crank is allowed to pound back and forth on the case and bearing, not to mention causing excessive movement on the rod and other moving parts. If the seal was incorrect or did not seal correctly etc., the problems that would cause, dirt in and oil out! With those parts missing or wrong its obvious it was "worked" on and if you have not had it opened up I urge you to do that before just putting those parts on. the bearing really needs to be looked at if it was run this way at all and probably put on the list of parts to change. The side cover also needs to be looked at really well, hopefully with the clip and seal missing that means that they may have been smart enough to remove them before trying to get the side cover off, but the fact that the parts were left off and it was being run that way......well that says whoever was working on it lacked some common sense :laugh: The bearing is retained to the cover via some washers and screws, and it needs to be securely mounted to the cover, if not the clip wont do anything as the bearing will just be locked to the crank and bang back and forth in the side cover along with the crank.
for future reference, all the parts numbers you are looking for are mostly found on the parts explosions that are easily found on the internet at major retailers (like partstree or jacks small engine) The actual photos and the way they are listed are confusing though as the drawings are generalized, and may be scattered between different sections, your clip and seal is a good example, the seal will be listed in the main explosion, but the bearing are clip are in section 2.
The other thing is if its not listed in part numbers side, that means that means it did not come on that particular engine even though it may be shown on the drawing.