You can make your own with a little work. Best place to look is over on the
www.gt40s.com and search for swirl pot. Several guys there have done them.
Basically a 1 gallon jug with 4 ports. 1. input from maintank pump, 2. outlet to main EFI pump to engine, 3. return line from regulator, 4. vent to main tank. With this setup the pump from the main tank only need to keep up with what is actually burned by the engine so a typicaly holley pump works fine.