What kind of bulk cable?
For canare or belden, any of the regular supply houses will do. There is often surplus bulk cable on ebay but availability is unpredictable.
If you want teflon insulated silver clad wire, there are several vendors that offer that. I found a place that sells the milspec silver clad teflon insulated 4 conductor cable in a wrapped teflon sheath for ~1.37 a foot @ 100dt and $.97/ft at 250ft. That is about 1.20/ft less than the next cheapest place I found of the 8 or so vendors I called. Unfortunately, my notes are under a pile of shit on my desk but I'm trying to find them for someone else here so I'll post them when they are found.
If you want a better deal than that, there is a guy who regularly offers the same basic silver/teflon/shielded/wrapped 5 conductor cable on ebay starting at 19.99 for 100ft. Some people may be hesitant about the 5th conductor, but I have a hard time believing that anyone could identify an audible difference between the 4 and 5 conductor wire. The audible effect is mostly from the silver, the teflon, the quality of the shielding, and the quality of the assembly. If you can properly assemble cables, it's a great deal.
For someone without good assembly skills, the custom silver clad cables you can order from guys here on TS are the best value and they will have a resale value that your own cables will not have.