Here's my notes from when I was researching replacing a Rockshox 21R on a GT Pantera for my girlfriends new commuter build:
(IIRC, I measured it at 430mm, and it was an 80mm travel fork, but I could be mis-remembering, 440mm seems to be a common replacement size for this, but as noted there are 453mm forks available as well.)
Kona Project 2: 60-70$, ugly?, eyelets, crown hole, no disc tabs, 440mm, 1040g/813g(triple butted)
disc tabbed http://www.cycle-solutions.com/Project-2-26-P4797.aspx
IRD MTB CrMo Canti rigid 26" 440mm fork
96$ IRD 440, 40mm rake, black, unicrown, 907g, eyelets,
$103 for Soma, canti, 40mm rake, 440mm length,
One One Inbred fork is 440mm.
Van Nicholas VNT TRX Alloy MTB Fork is only 420mm
IndyFab no-Travel fork is 430mm for 80mm fork replacement.
She doesn't really ride in foul weather, so I have yet to tackle the MTB conversion build, I've still got my fingers crossed that the fork I picked up will end up matching correctly, given I had to guess at how much it compresses usually. I'll dig it out of that parts box tomorrow and post which one I chose. I want to say it was the IRD, which it doesn't look like they are offering right now, but could probably be tracked down somewhere.
EDIT: Yeah, this was the fork I got --> IRD MTB CrMo Canti Fork Black, 1-1/8" Threadless, Cantilever, 26", 440mm fork, 40mm rake, black, unicrown, 907g, eyelets, 96$
I might have some more notes in an earlier draft of my research for her bike that I edited out as I narrowed down my search. If I come across those, I'll post them up too. Hope this helps!
Here is some errata from my research, quotes from sources all over the internet that I was using to inform my decision:
" Kona and Surly forks are too short at 410mm, unless you want crazy twitchy handling. Vicious and Salsa are the only two currently available that (I know of that) are the correct lenght 425mm (or so). "
" Surly 1x1 100mm for is 453mm long which would make the HT angle about 1 degree more slack, one set of eyelets, rim brake mounts, the disc caliper mount, and the line guides but it is corrected for frames designed for 100mm suspension forks. Straight blade."
" The 21 R uses the Mag fork brace, MCU spring, SL crown to give 60mm of travel while weighing in at 3.0 lb. "
And a note to myself about forks I found that I coveted, but were too rich for my blood:
Vicious Cycles forks are very expensive i.e 275+15 for fender tabs + 60 $ for low rider rack mounts, Straight blade.
All that said, I wish I knew about the Troll fork when I purchased the IRD. The Troll has mid fork eyelets and double eyelets down low, making it easy to mount both fenders and a variety of racks, and cleanly at that. Myself, I'd be tempted to cut off the disc tabs and repaint it, but then again, I'll probably experiment with discs up front at some point on one of our rigs.