Try your local auto parts store. Some engine assembly lube used to be heavy molly grease. STP was heavy in molly, but would be a little thin.
Whats the issue with Graphite?
The theory is galvanic corrosion will start between the steel barrel nut and the aluminum receiver since graphite is conductive. However the anodize coating on the receiver threads is not conductive at all, so unless that gets broken through into bare aluminum it ain't gonna happen.
