He has a store on cafepress:
The Joe Store. 3 years ago, he started selling collected editions of his B5 scripts. You had 5-7 scripts in them with and introduction that would get longer 70-80 pages or so. It was a 15 volume set, and concluded publishing earlier this year, and will never be reprinted again.
He was also able to get a deal with the writers of the other episodes and they were published in a 3 volume set called "Other Voices". Right now, he has a chronology of Babylon 5 available, where it covers all the episodes, tv movies, spin-off series, novels, comics and short stories set in the B5 universe. There's also a B5 quote book which was supposed to been released years ago, but the publisher went out of business, so that's available as well
There are plans for script books for the spin-off series Crusade, which will include the writer's bible which shows where the series was supposed to go, and plans are in the works to republish his 3 novels.
Comic wise, pick up Rising Stars. It's excellent. I'm iffy on the 3 related mini series, but the main series is worth picking up. And last I heard, he's still working on a Babylon 5 graphic novel