It's done. Went with Discount Tire because they have a nationwide presence, and opted for their replacement certificate ($23 per tire) which will provide a ten year/50,000 mile replacement if we lose another one. With the Minnie already 15 years old, it's likely these are the last tires I'll need to buy for it.
My mixed set of tires wound up being 2 Uniroyal Laredos from 2009, two BFG Commercial TA's from 2012, a Cooper Discoverer HT from 2014 (kept as the new spare), and a Michelin from 2004 that came with the motorhome as its original spare (put on about a month ago when I lost another Laredo).
Feels good having a matched set, and I feel a lot more comfortable taking it out to Wyoming and Colorado next month.