Did you try American Autowire? I recall that they have a couple different bulhead connectors and they just supply the bits and pieces form so you can make a proper harness.
I do a good amout of wiring and i never run anything thru the firewall, i drop down and come up under; the headlight/turn signal i split back at the firewall so that each run forward thru the right and left frame rails and stub out at the lights and this avoids that nasty cross-over under the radiator.