Help with Scanner/Antenna adaptor....

[MacBaine]

If anybody here is into radio and/or electronics and whatnot, maybe you can help me. I have an old radio shack PRO-25 scanner with a screw in antenna. I have an antenna on my Crown Vic PI which I would like to somehow wire to the handheld scanner until I purchase a car mount scanner. The thing is, the antenna adaptor on the scanner is about 5/16" (crudely measured) and the antenna adaptor is a 3/8 BNC connector. Both are female. I looked around at radio shack, but they dont seem to have any connectors that are threaded for the 5/16" or whatever scanner plug. I was thinking I would probably have to buy a short length of cable and build my own with 2 different ends. If anybody here is knowledgable in this area, any help/tips would be appreciated. Thanks!