Re: 4/3 Tasha's AMPS 397, +3 267
A lot of people here feed either Friskies or the Classic variety of Fancy Feast. (FF changed the name of the low carb, pate style food. The names on Janet & Binky's list doesn't reflect the name change.)
Petco is closest to me so that's often where I shop if I don't get things on-line. (I usually get food and treats from PetFood Direct.) They do carry the Wellness jerky treats, Purebites freeze dried chicken, and tuna flakes. They also carry several of the Catswell products -- they are a jerky-style treat. With treats, you just want to check the label to make sure that all that's in the treats are a protein (chicken, beef, fish, etc.) and maybe some vitamins or other nutrients. Check one of the brands against something like Temptations and you'll see the difference in content. Generally, freeze dried or jerky-style treats are the best options. Also, you may find the freeze dried treats in the dog treats aisle.
Karo is fine to use. Many people here who have cats that are either gluten sensitive or have a cat with a delicate system will opt to use Karo over a gravy-style food. You just need to keep in mind that only a few drops of Karo will bring numbers up. Depending on how carb sensitive your cat is, 2 or 3 drops of Karo may do the same job as a teaspoon full of gravy.