The lock is Trimark.
Replacement part number is 13438-05, which is chrome handle with black surround. Polling a few places, it is apparently not available.
The 13438-04, which is black handle and black surround, is available from several sources.
There is a newer 030-1450 Trimark lock which has slightly different size dimensions, which would possibly require modifying the linkages and such. I am going with the 13438-04 as a drop in replacement.