Wire wrap is close to being obsolete, but this Wikipedia entry is a pretty good explanation:
https://en.wikipedia.org/wiki/Wire_wrap
When I installed a Studer TLS4000 synchronizer back in the early 1990s, it came with a custom made card to interface to the A820 it would be used with. The card was constructed with wire wrap, probably on an automated machine at Studer. Since demand for these cards was fairly low, and each model of machine needed a unique card, it made sense to manufacture them as they were needed, rather than make a batch for stock.
And sorry, I don't have a source for materials.
Geoff