I've got the same question as I'm probably going to put an SR20DE in my next circuit car. I remember that Converted used an R33 5 speed behind his SR20, can't remember why that was.
Maybe you could use an R31 5 speed from a Skyline or Crummydore. The old reliable R30 stumpy box comes to mind as well. I have been told by Stewart Wilkins that the 5 speeds out of Navara is an option as well. I have the standard SR20 box still (have had the engine since 1994) but the amount of cutting & fabrication around the back of the box means I'm probably going to use it as a source of the front half, unless I can find a Drifter who's blown up a gear box & is willing to sell me the remains.