Interesting... I just downloaded the software from Nortel's website less than two months ago, but now it's not there.
Unfortunately, I think this forum is limited to posts only - no software exchange, so I can't get you the software (software is free, the licenses are up to you).
At this point, I immediately start speculating... if we have no access to the softphone, does that mean they are doing away with it? At a recent INNUA conference in Tempe, AZ, Nortel announced that they are pleased to be included on Microsoft's new desktop, being released this summer, as the default SIP client (an improved alternative to the 2050). Are they pulling the carpet on the 2050 to re-direct their resources into the Microsoft project? hmmm...
The only thing I can think of for getting build 385 is to talk to your Nortel Account Rep.