476mm a/c = 100mm travel 26"

Your suspension forks should have about 25% sag when you're riding it.

When your fork is set at 25% sag it will have a a/c measurement of about 450mm

Something like a 100mm Surly 1x1 with 453mm a/c or a Surly Instigator 1.0 with 447mm a/c is what you want.

http://surlybikes.com/parts/forks/1x1_fork
http://surlybikes.com/parts/forks/instigator_fork