I find this wiring-sleeve weave stuff most handy. Or I call it boat rigger's weave, or Chinese finger-trap weave
I get it in various sizes and colors from these guys. It's affordable in bulk, and a roll lasts me a long time, they will indeed sell to the public. Makes the project look nice when it's done too.
Like in the picture, when combined with a bit of heat shrink tubing, it makes a custom wire run look better than factory.
Ps: Harbor Frieght sells a great heat gun for like $8 bucks.