Sounds like you're looking for a female BNC-to-male RCA adaptor. You would think they should make this and have it at Radio Shack. Exasperating.
As a temporary fix, Radio Shack does have male BNC-to-female RCA adaptors, and you could plug a male-to-male RCA adaptor into that to create a BNC-to-male RCA adaptor. Alternatively, you could use male BNC-to-female RCA adaptors with male RCA-to-RCA cables, both from Radio Shack.
Best of luck with your custom solution.
As a temporary fix, Radio Shack does have male BNC-to-female RCA adaptors, and you could plug a male-to-male RCA adaptor into that to create a BNC-to-male RCA adaptor. Alternatively, you could use male BNC-to-female RCA adaptors with male RCA-to-RCA cables, both from Radio Shack.
Best of luck with your custom solution.