There are two places in Central MS I've found that still carry 13" tires for the Sentra. One is here in town, but was closed today. Seeing as how the problem had gone from bearable to scary, I had to find if Sam's actually had any in stock.
Funny story, the guy said. Normally they had to order them, but since they'd sold a few sets somone in Central Purchasing (I imagine) sent them some finally. 24, in fact. . Normally they go months between selling a single set, mind you. So I got three new ones at 3.30 on a saturday afternoon.
This is the same car that when I bought the new Windshield wipers not five minutes before a storm, it quickly stopped raining, and within the hour got bright and sunny, and stayed that obnoxious way for nine solid days. Not a cloud at a single moment, much less rain.