Hiryu in Capcom's Artbooks
Gamest Mook, Vol. 17: Capcom Illustrations
???
This was the first officially released Capcom artbook, featuring two pictures of Hiryu: the two below. They're good pictures, classics... but they're not worth the $100 USD you'd spend on eBay trying to get the book.
CAP! FanBook
???
This is issue five of an exclusive members-only Capcom fan magazine. It's very rare, as it was never intended for retail sale.
Capcom Design Works: Early Days
Jan. 8, 2001
This is a re-release of Gamest Mook, Vol. 17: Capcom Illustrations. If you're a diehard, you're lucky. The re-release makes it easier to find and less expensive to buy. You can find it at BeNippon.com.
Capcom Design Works
Aug. 1, 2001
This is somewhat easier to find than the others. Buy it! You can find it on Play-Asia.com.