@Jeff Brown Buy the official replacement SD card from PacParts.com (Pioneer QXX3352), see https://www.pacparts.com/model.cfm?model_id=AVHW4500NEX&mfg=Pioneer&back=0&action=list_part. $95 + s&h.
BEFORE YOU INSTALL the new SD card, clone it to an image on your hard drive and back that image up for safekeeping. As you hopefully already know, the SD card will be locked after you install it, and no one here knows the SD card lock/unlock password yet.
I just did this with my own 4500 (with a slight twist). I cloned the QXX3352 SD card, and then put it back in the packaging