I believe what may work is the old school wide-type canti. The only current one I know if is the Tektro CR720.
http://www.tektro.com/02products/11qb.php

What you need is mechanical leverage.... and these type have a ton of it over the Oryx or any other "low profile" canti.

I also use these brakes on another bike. 80's Deore BR-MT60. They don't look like much...but they have oodles of stopping power! I found a nearly new pair on Ebay for a spare set for about $16.
http://www.velobase.com/ViewSingleCo...47b8f&Enum=117

You may also try the NOS Suntour XC Pro Canti's. The are quite adjustable. Not quite the leverage on narrower canti mounts, but if you move your straddle carrier cable high and make the arms as wide as possible it works fine. They are always for sale on ebay .http://cgi.ebay.com/NOS-Suntour-XC-P...3A1%7C294%3A50