Tried finding a comparable fan with similar specs (size, CFM rating, 2 vs. 3 
wire?)

I have a Nidec TA450DC series, and I noticed when I looked at the page for 
them, they implied imminent if not already discontinued.  I'd look at their page 
(it was an easy Google IIRC), and find a close match locally.  Nice fan-- 
heavy metal case, low draw for the rated CFM.

Perhaps you can get some more life from the fan by peeling the label and 
oiling there.