Wish I knew, I look around from time to time on ebay or swap meets, but so far I have been buying Painless wire from which ever vendor has what I need shipped the cheapest.
A dozen spools of TXL wire would not be cheap, and I do enough in the engine compartment that the 140F rated "hookup" wire isn't much use, but this place "looks" interesting.
http://www.oemsurplus911.com/calterm/calwire.htm
Here is a snip from another forum on wire.
Not all wire is created equal. For an automotive application, you shouldn't just buy any plain old wire. I would recommend a cross linked insulated wire, commonly GXL or TXL.
From Waytek:
"The SXL has a standard wall jacket, while the GXL has a thin wall jacket
and the TXL has an extra thin jacket. Because of its ability to withstand high
temperatures, all three are typically used in high temperature areas such as
engine compartments."
Painless and other harness manufactures use cross linked, and Painless uses TXL. Relative cost is GXL cheapest, TXL in the middle, SXL most expensive. If space is a concern, use TXL. All will function the same. You can buy Painless TXL in your quantities from any Painless seller or Summit, but it is nearly three times as expensive.
Other considerations: Pico brand wire spools available at some auto parts stores, such as Car Quest, (though I don't know if it is cross linked) are at your quantities and is very good wire. Summit sells the same stuff under their Summit brand in 100' spools. I am not real positive on the stuff you get from Napa (though I don't think there is anything wrong with it except that the insulation is very thick). Do not buy wire from an electronics supply house, as it is not intended for automotive or harsh conditions.