Can anyone suggest a brand I might try? I've looked on the Web sites for
Science Diet, Iams, Eukanuba, etctera, but I haven't seen anything that
specifically says "low residue."

My cat had this. I gave him Katz n Flodder (sp?) dry food. I also made plain
baked chicken with enriched wild rice mixed 50/50. Chop up chicken with skin
and fat into bite sized pieces and mix with rice. Store in small containers in
freezer and defrost as needed. You might also want to mix some vitamin/mineral
powder into it. It'll take two days for her stools to get better. Don't let him
eat anything else, not even a bite or he could end up with the bloody mucousy
diarrhea for three days. My cat had the extreme type.