They are on Ebay all the time. Some work most don't. You will need to get the Dodge truck antenna (unavailable, not made anymore) to get out put and radio to work. Most radio shops will "not" repair the CB/AM/FM combo units. These radio set ups were not very good for CB use at the time of manufacture. I would recommend if you want to use a CB, get a Midland mic combo unit and put the brain module under the glove box cavity. Also standard CB antenna coax will not attach to these factory radios.
Here's some photos of an antenna for a Dodge Van CB/AM/FM (still available on ebay)
modified to fit the Dodge truck fender ( you will need a host of stock mounting plates , nuts to covert & welding skills).
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AM.CB. system2 photo.jpg [ 190.38 KiB | Viewed 11244 times ]
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AM.FM.CB. 1.antenna installation.jpg [ 212.02 KiB | Viewed 11244 times ]
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CB enhanced Antenna mount.jpg [ 200.01 KiB | Viewed 11244 times ]