I found a ebay auction on Bountiful Baby’s home page that’s is listed for 3 month old Realborn Joseph prototype! Here are the links below:
Bountiful Baby’s Home Page: Link:https://bountifulbaby.com/
3 month old Joseph ebay acution link: https://www.ebay.com/itm/reborn-doll-baby-boy-Prototype-Realborn-R-Joseph-awake-3-month-old-Toddler/323639846822?hash=item4b5a7027a6:g:I64AAOSwXc9cNASR:rk:2:pf:0
Bountiful Baby has a new belly and back plate the especially designed for him: Realborn® 3-6 Month Chubby Belly/Back TORSO for 23-26" Dolls- #3599 - Bountiful Baby (DP Creations LLC)