Well congratulations in advance then!
RG8 is a generic term for a particular kind of cable.
Being as you're in Miami, this place might be able to hook you up:
Nemal Electronics International
12240 N.E. 14th Avenue
North Miami, FL 33161
Telephone: (800) 522-2253
http://www.nemal.com/
I've no idea what their sales policy is but you can just tell them you're looking for X feet of RG8 type cable. They may have several variants. Just tell them it's for an audio application and you're looking for something that balances flexibility and low capacitance.
Mind you now, I'm not saying you'd be able to tell the difference in double blind test...