annoyedLowe's took it back (generous of them given that I'd lost the receipt, but they found it in the purchase history on my Lowe's card), but to our annoyance didn't have the equivalent kits for 3-inch toilets, nor did the other place in Fernley like to have such things. Therefore, it's off to Reno/Sparks when we can get in early enough in the day on a weekday to one of the specialist plumbing stores.
Fortunately, we have two (normally) working toilets in the house, plus the one in the travel trailer, so we're not in a crisis at the moment. It's just another one of those homeowner annoyances.