My first thought is Mouser Electronics in Texas. Another possibility is cablesonline.com, located in New York.
I have used Mouser Electronics before, I did not know about cablesonline.com
I will look at Mouser first. Because it is closer.
There were 2 styles that I have used, one had a ring of foam around the wires inside a vinyl jacket and another that had foam around the wire and between the wire inside a vinyl jacket. That means the dialectric properties were better with the foam between the wires too. Last time I used it, it was rated at .7 db loss/100 ft. up into the UHF range. No coax comes close to that. Not even Heliax.