As another person responded, the Mopar trunk lid weatherstripping may still be available as new, old stock on ebay if you want to search under the part number from the Parts Catalog for your year (pdfs in the Service Information subforums here). However, it will probably be quite expensive on ebay or from the online Mopar parts websites. So the best alternative is obviously to check a junkyard for one that is still good and not deteriorated. Some junkyards may even be able to order one from another junkyard if they are in a used parts network (be sure to give them your exact car year/model).
If you can't do that, there is a much less expensive solution, but takes a bit of careful work. Some of the better auto parts stores sell rolls of car weatherstripping in different cross-section shapes and sizes. You want the actual firm weatherstripping, and not the very squishy open-cell foam that they may also sell. Some NAPA and (few remaining) Car Quest stores may even have big rolls that they can cut to length. Take in a drawing of the trunk weatherstripping cross section (height x width) and approximate shape, to get the size you need so it will seal when the trunk clamps down. (They used to have a big paper catalog that showed the cross section shapes.) They do come in package rolls with different lengths, so you can only buy as much as you need to save money. Amazon does have it, but a lot of what they carry is cheapo imported junk that won't last, so I'd check the auto parts stores first.
To glue pieces of this in place, they also sell special car weatherstripping adhesive by Permatex, 3M, etc. It comes in yellow or black - get black or the yellow will show in the glued seam and look messy. It is like very strong contact cement (read instructions). It actually comes in regular and "super" types, with the super weatherstrip adhesive a bit stronger, so get that if they have it. You can search on weatherstripping adhesive on Amazon under automotive section to see the types/brands.
Then, if you have areas where the trunk weatherstripping is missing or deteriorated, you can cut these out with a sharp Xacto knife or box cutte) with some cardbord underneath (wear gloves). Then per the adhesive directions, carefully glue a replacement piece in place with adhesive on both the metal and the original weatherstripping on both sides so it won't leak through the glued seam. If you do it carefully, it will look OK. Also use a small amount of the weatherstrip adhesive to hold the original trunk weatherstripping in place on either side of the repair, and wherever it is loose around the trunk opening - feel all around and see if you can easily lift it up off the metal lip. Obviously, don't close the trunk down on it until the glue fully dry per the instructions - if the car is outside you can obviously use some rope to close the trunk lid most of the way down but not squish the weatherstripping.
