I found one tire--one--that matches the specification in the manual. It's $87 from one place and $97 from another, all before tax and/or shipping.
The bike has a 17" rear wheel, but I've got a spare which is 18". I might be able to find a less-costly tire that would fit it, but of course I'd then have to completely shake down the bike again. No idea if the bearings in that rear are any good, or if X many years of inactivity have turned them into lumps of iron oxide, so I'd have to swap the rear bearings, too. On the plus side, since the speedometer runs off the front wheel, changing the rear tire size wouldn't have any effect on the speedo reading.
...but the spare rims are gold. The ones on the bike are black. I'm not going to mix-and-match them.
Of course if I wanted to pay $300 for a rear tire I could probably have my choice of brands, then--but I paid $350 for the whole motorcycle. C'mon.
The tire size is 110/90-17. I've seen 110/80-17 tires; this makes the tire slightly shorter (thus has a smaller circumference). The 110/90 is 99 mm tall--from rim to crown of tread--and the 110/80 is 88 mm tall. So it ends up being about 2.2 cm smaller in diameter, which leads to a corresponding greater engine speed at the same road speed. And the thing already screams like a banshee as it is. *sigh*
And while I'm at it I looked up how to decode the DOT date code. This tire was made in January of 1991. It's old enough to buy beer. Shit.
So: tire, tire irons, rear brake shoes--this is an expense I was hoping to postpone. What a pain. Especially since I'm going to have to balance the thing, and that means either I take it to a shop or buy a fixture for balancing tires. *sigh*
UPDATE: OKay, I can find two:
The first one I found--in several places--but this one has the cheapest price I've seen at $83 with their $5 "tire fee".
The second one, which is a Bridgestone tire, for $83.
All else being equal I'm tempted to go with the well-known name brand, you know?