As everybody knows, the continual conversions of half cabs to full cabs has made the once-frequent RFW on the 
a rare experience. However, the fact that so many of the 17-18xx cars have left means that a higher percentage of R62As carry RFWs than before (i.e., if it's not an R188, there's probably an RFW somewhere).
As of today's fleet set-up, there are two trains with 6 single cars and a 5-car set.
Those trains are:
Flushing : 1934-1921-1924-1918-??-?? Married Set : Times Square
Flushing : 1901-1922-??-??-??-?? (no set attached) : Times Square
There are two trains with Manhattan-bound RFWs, which is a rare occurrence. I rode one of them from Flushing to GC, fantastic ride.
Those trains are:
Flushing : 2080-2076-1914-2015-2011 : Times Square
Flushing : Married Set-??-2070-2066 : Times Square
Also a handful of Flushing-bound RFWs on various cars. Many more have been converted, though.