Need Female BNC to Male RCA 90 degree adaptor...?

You could get a cable with RCA on one end and BNC on the other or get a RCA right angle and a straight BNC to RCA adapter. 

Right angle connectors are not great. Avoid that if at all possible. 

I work as as AV professional and have never seen that exact 90 degree configuration.  You can easily do it with two adaptors however - RCA F to M 90 and then a straight F BNC to M RCA. The depth (at the 90) would be the same, just a bit longer in length.  Or, you could reterminate the cable end to an RCA.

Thanks guys, your feedback is much appreciated