try calling speedotron direct. they have great customer service and do the repair work as well. at work, we've have had a couple of theads & packs rebuilt by speedotron in Chicago--fast turnaround, great service.
fwiw, by "plugs", do you mean the metal connectors--multiprong female that goes to the power pack? I'm wondering what you did to it to mess it up or why you would need backup spare parts...sorry, we have 8 heads or something like that, for over 16 yrs and we've never had that happen.....now, we have had 2 heads explode & totally become destroyed. Had a power pack implode and be fixed *twice* under warranty....we have a head with the power cord duct-taped into it....have had to replace a power cord or two to the pack...but NEVER have we had a connector fail....
seriously--call speedotron. by the way, those heads & packs put out alot of juice. If it were me, I'd send the head back to them for the work. be safe--I've seen one of those heads explode, and it ain't pretty.
good luck, KT