INFI is a proprietary steel. Only Busse uses it. (there are two other Busse Kin companies that occasionally get INFI, Swamprat and Scrapyard).
Tons of options for Bowie knives, and no reason to limit your self to Busse.
Branch out and get a custom. Custom makers abound on the custom forum.
I don't really know an INFI "equavilent" steel. It is fantastically tough, a ND stain resistent. Decent edge retention.
Lots of other super steels out there will preform for toughness, and some have better edge retention. If you want to spend the money.
I've been more than happy with the performance of all my knives from Busse. They have a knack for getting top performance out of what ever steel they are using. (that applies to Swamprat and Scrapyard too).