Rhode Island Wire, carries it by the foot and great prices. They also carry original cloth covered wire for vintage vehicle restoration in different wire sizes and color's with or without tracers. I build all my harnesses using their products. They also carry wire ends to include the bullet wire ends that are used on the HT and also the connectors. They only do orders by phone, but they have an online catalog with wire types, etc. and pricing by the foot.
Markus