I used to have great success on my Nepal treks with the basic ACE Brand Knitted Knee Brace w/ Side Stabilizers ($8 each at Walmart). Be sure to upsize one size bigger.
Now I use the KT Tape Pro Extreme Therapeutic Elastic Kinesiology for even better results (but more pricy than the reusable Ace braces). They lasted my entire Three Passes trek in Nepal 3 months ago. I didn't even feel them (be sure to shave your skin first).
Good luck.