IIRC I have dealt with this on this one srt8 grand. it came in twice like 2 weeks apart, both times the antenna assembly missing. The base that has the cable attached to it is going to be down in your fender. if you get the base and an antenna, so long as there is no other damage done, you should just be able to screw the retainer on the base (that screws to the guts currently dangling in the fender) then screw the antenna to it and viola.
If you call your local dealer's parts department or look on j4j you need the following part numbers.
56038725AC antenna mast
56038729AE antenna body cap
56038730AC antenna escutcheon
(numbers 1-3 on the above picture)... should not be too bad. im not sure if there is any ferrous metal in the base assembly so im not sure if a magnet will even work, I will say I have fished em out a couple times through the gap in the fender to inner fender with the hood up... it may be easier to pull the fender liner out (not sure).