Dave,
I haven't heard of any for your diff (short nose R200), but there are some for the long nose R200 (I believe a 3.15 R&P set is available through Kameari in Japan, and the 260Z 2+2 manual or the 79 2+2 4 speed come with a long nose R200 3.36).
An option would be to go with the R230 diff. R230s are available on Nissan Armadas (2.9375) and 300ZXTTs (3.7). Armada diffs are a little harder to come by, but if you're able to get a 300ZXTT R230 (easier to come by), you can probably swap in the Armada 2.9375 R&P set which is $295 from Courtesy Nissan (contact speeder on this site...he's doing the Armada R&P set into 300ZXTT R230 diff conversion).
Check out this link:
http://forums.hybridz.org/showthread.php?t=106621&highlight=armada+r230
I have some 300ZXTT R230s available for sale, but shipping might be expensive (these diffs are over 100 lbs). There's one in the classifieds that's a little closer to you, which is being sold by J. Soileau RB26zcar. Here's the link:
http://classifieds.hybridz.org/showproduct.php?product=3440
Good luck on your project!