Where can I get cable to plug amp in stock HU?

See title :) I need to find out where I can get a conversion cable to let my stock HU to accept the RCA jack from an amp? Any ideas? Local stereo place?

PAC OEM-1 (http://www.affsave.com/pac.htm)

check if your amp accepts speaker-level inputs. It'll save you a bunch of $$ on the adapter for the deck.

Thing is, I haven't bought an amp or a sub yet. My idea was to get the stealth box, with a 10" and an amp( no idea where to put that lol) if anyone has any ideas, please toss em at me! I'm looking to spend 300 maybe?