HH,
I don't have exact numbers, but the MR2 certainly flew one during its final few months in service all the way out to 26W looking for a vessel that the Canadians thought they had heard call a mayday. Satellite info was inconclusive (single hit) so we launched as fear was vessel may have sunk.
Turns out we didn't find anything of note, but that was because the vessel in distress was in the southern and not the northern hemisphere. Mayday call was so weak it was difficult to make out the latitude clearly enough.
During my time on the kipper fleet, there were probably about half a dozen a year on average that extended beyond 15W although I'm sure the ARCC will have accurate info if you ask them nicely?