I read that lean raw meats like beef and pork are the highest in thiamine, but all meat contains it. Egg contains thiamine too. Hearts and gizzards also supply B vitamins, including thiamine, but not a lot. I am not an expert, but feel fairly comfortable with the feeding regimen I've got going now.
Jennie and Queen Eva get a 1.15 (give or take) ounce prey model meal every other day, containing a muscle meat, liver, and egg shell calcium. The meats in rotation are beef (cut depends on what was on sale when I bought it), chicken breast, chicken thigh, turkey breast, turkey thigh, chicken gizzard, and Cornish hen, all parts.
Those two get Stella & Chewy's usually three meals a week. Jennie gets a bone in wing part on Sundays. They get raw egg yolk (balanced with egg shell calcium) once a week. Queen Eva gets one ounce of Rad Cat daily (three proteins rotated)
The rest of their foods are canned, the bulk (up until now) being By Nature Organic, chicken, turkey and turkey&chicken, with Jennie also getting some Weruva (until it is used up) and Tiki Cat. Other brands come and go, the current extra brand being Wild Calling.
I am still using up, very occasionally, some Castor&Pollux and Natural Balance. They love the stuff but it is very high carb (both brands) and they both contain spinach. When it is gone it won't be replaced, but I can't afford to give away any more food. And the poops after they've had those high carb foods..PEEEEEEEE-EWWWW!
I've just read that beef liver also contains a lot of thiamine. I use chicken liver. Hmm...maybe I should rotate that with beef liver..the freezer section at my grocery store does carry it.