Most mophie products do not have replacement parts available. This means if the top cap for your juice pack is cracked, a watch stand is broken or a cat chews through the charging cable for your charge pad, there is no option to get just that individual part. You would need to replace the entire unit by ordering a warranty replacement here.
However, there are some products that use a universal charge cable such as a USB-A to micro-USB, USB-A to USB-C or USB-C to USB-C cable. Those cables can be found individually here. Check your User's Guide for the specific type of cable used for your product.