The 759-04047 is the current part number for the 50" blades. Not sure why the 3 pack at Partstree costs more than getting 3 individual blades? CNG (Bermuda Ken's dealership) has the 04047's online for $19.42 ea. You should be able to sharpen the old blades up on a bench grinder and get enough time out of them until the Gator mulching blades are available, they do list a 50" size for CC at Gator but I'll take it they won't fit the 2550 deck for whatever reason. I just put a set of the Gators on my 44" and they work great, and were only $13.00 each on E-bay.
-Fordlords-