best source for a high quality thermostat

The last high flow I got was a Mr gasket, which failed in short order. I have one in my notch 340 that`s been in there for 20+ years.
I went to auto zone and asked if they had a high flow for my 440, they only had a Stant that looked like a normal stat, but is supposedly a high flow, Installed and has been working good for years.