Looking for sources of raw material for my Thing-o-Matic and soon, Mendel Prusa, I collected a number of links to sites in the US. I typically use 3mm ABS, so that is the focus here.
The best price I found was for a 12 lbs of air-spooled black ABS plastic from buy3dink.com for $70. I was a bit concerned upon it’s arrival as there was a distinct odor emanating from it. It must have been the freshness of the extrusion, as it dissipated after a few days. Other than the odor, it was a bit challenging to spool it up for bot use, but I bodged something together with an old bike wheel to keep a steady rotation as I spooled it onto a reel I bought from Home Depot (same as the item linked below). I also bought a 5 lb air-spooled roll of safety-orange 3mm ABS, and a 1 kg spool of white 1.75mm ABS for future experimentation.
The orange and black print well through my TOM. Shipment was quick. Recommended.
I’ve also used Makerbot. When I bought my printer, I also bought some blue, natural, and glow-in-the-dark 3mm ABS. All of these worked fine, but without a spool, it was difficult to work with. Since then, Makerbot has started shipping on spools, of which I bought some black, green and red. These spools work well with Thing 7105 to mount directly to the Makerbot.
Many colors, on spools, quick shipment. Also recommended.
Others that I may try in the future: