Carl, I've personally tried remotes from RCA, Zenith, URC and my favorite, which is a Chinese no-name, and not a one of them had a code that would work.
The URC, however, could be "taught" to work the box, you just have to go through the fairly tedious learning process. There are a number of "learning" remotes out there, some cheap, some not so cheap. You pays your money and you takes your chances.