There are some companies that make replacement connectors, generally with a "pigtail" attached, that supply those auto shops. What I've found is that the auto parts stores often won't bother even looking for stuff that isn't a high-demand part (like pigtails for GM alternators or headlight connectors). If you Google the part you need often times you can get a part number to give them. I've had good luck with RockAutos catalog. If that doesn't work I use a local electronic's store; often they will have the terminals I need to rebuild my connectors. If all else fails there's always the pickapart style junkyard.