Pete, have you tried the West Systems 610? It is already a thickend epoxy that is way cheaper then other cartridge dispensed epoxies and it uses a regular caulking gun to pump it out. I use it all the time for filled bonding areas and you could mix in other fillers as well. I don't use the supplied tip and just apply it with a artist's palate knife.
Are you looking for short stranded carbon 1/4 inch or milled carbon like power? I can put you onto the 1/4 carbon but don't know a spouce for the milled powder type like cabosil powder.