Tecumseh had quite a few models of OHV engine, and I find their technical manual difficult to identify models from (I can't find any reference to a model number beginning with OV followed by a number), so I tried another approach and looked at their parts list, here:
http://www.jackssmallengines.com/Jacks-Parts-Lookup/Model-Diagram/TECUMSEH/134885/41205

That way are looking specifically at the Model OV358EA, and no other. If you slide down to the bottom of Slide 2, you see this:
[Linked Image]
This does not show a thrust washer on either end of the camshaft. It does, however show one at each end of the governor shaft - see Item 80:
[Linked Image]

I am forced to conclude that the references to the washer that I found in the tech manual, were for a different OHV engine. That would help to explain why your engine, which looks as if it hasn't been apart before, does not have a washer on the camshaft. Can you help substantiate this reasoning by showing us the end of the camshaft, on the opposite side of the timing gear from the lobes, so we can see how it is supported?

It is interesting that the US parts store shows new camshafts as available for sale, by the way.