It's a typo.
He meant
IA8, meaning
Imperial Armour 8: Raid on Kastorel-Novem which is sold by forgeworld. It's the book containing rules for all the ork units sold by them, plus a nice campaign, great art and nice fluff.
However, that book is out of date (written for the old codex and 5th), so I wouldn't recommend buying it at this date. Maybe after they have updated it, if they ever do.
Parts of that book can be gotten free here:
http://www.forgeworld.co.uk/Downloads/Product/PDF/d/Dred_Mob.pdf In general, the Kustom Stompa has many out of date rules, you'd be better off using the stompa from the codex or the bigmek stompa from the most recent
Apocalypse book.
Some people use the kustom stompa to get the codex stompa for less points while using the improved weapon profiles from the codex.
IMO this is bad sportsmanship in the very least, if not cheating.