Not "manga-sized," whatever that means, but Palladium games are available from B&N:
BN No Results Page
m.barnesandnoble.com
Well, the item linked is listed, but like the vast majority of things B&N lists, it's out of stock online. When I check it to see if any store within 100 miles of me has it, I get a lot of stores but none that carry the item.
But no, the thing was that when Palladium relicensed Robotech, Kevin had what looked like a classic Unca Kev moment. He declared that all Robotech fans were craving a "manga format" book (A5? size). Then the feedback came in and it was overwhelmingly negative. Still, Unca Kev insisted the fans were on his side and pushed forward.
I figure it was because of some discount he would get on printing or perhaps some kind of requirement of the license. It's also possible that he was in talks to get B&N to put Robotech RPG books on shelves, but they'd only do so if the books were the "manga sized" form factor. Who knows?
Whatever the reason, the later books in the line didn't get a "manga sized" treatment, and the format didn't expand into other Palladium books lines. The manga sized books were reprinted in full size.