Should I put the tcl files into the cell library search path or something?

The

source

command is pure Tcl code, so it's just processed by the Tcl interpreter and doesn't have anything to do with cells. There's an

auto_path

command in Tcl that could be used, possibly, to make a copy of the cell path list so that

source

searches the same set of paths.

Thanks for the answer Tim 🙂