Fel Pro thermostat gaskets?

Not quite the same - Hylomar is a solvent-based non hardening blue goop. The nearest locally available Permatex equivalent is #85420 "Fuel Resistant Gasket Dressing & Sealer". Smells and looks identical to genuine Hylomar.

If you really want silicone, you can also use their #22071"Waterpump & Thermostat Housing RTV Silicone Gasket Maker"... definitely coolant resistant ;)