On February 4, 2020, WB is releasing a compilation DVD entitled Saga of the 13th Ghost. The 2-disc DVD set will feature the entire 13 Ghosts series, as well as the Curse of the 13th Ghost movie. It is currently available for pre-order on Amazon.
Thanks to Scoobyfan4ever for sharing this with me!
Also, if you haven't already, be sure to check out the cool new forum that ScoobyDooUK (who is a frequent commenter on this site!) has created, scoobydoo.boards.net!