I don't think you can get just the sockets, need the rear fascia harness. Believe this is the culprit
www.stevewhiteparts.com
If you buy from Steve White, discount code CHA1 , there are listings at ebay as well
You could always splice one from the new harness to save having to change the whole thing, assuming the wiring is OK. You'd then also have a spare
A Guy
2008-2014 Dodge Challenger Rear Fascia Wiring 68039503AA | Steve White Parts
2008-2014 Dodge Challenger part # 68039503AA - Rear Fascia Wiring

If you buy from Steve White, discount code CHA1 , there are listings at ebay as well

Rear Lamp Harness Connector Mopar 68039503AA fits 08-14 Dodge Challenger | eBay
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You could always splice one from the new harness to save having to change the whole thing, assuming the wiring is OK. You'd then also have a spare
A Guy