there is a trd helical diff for sale on ebay think it was about 300.
have a wee search on there, 90% sure it was in japan too.
good luck
Phil
Ryan, those TRD ones listed on eBay might say 2 way but they are switchable to 1.5 way. Personally i would buy the TRD mechanical unit.
TRD mechanical. You can still buy them new from Toyota locally. Far better for straight line lockup, they are also adjustable via shimming for setting the agressiveness of the locking action. As on starletcentral they're about $1200 currently, they do come up on trademe for less than that on occasion