If you're going to get a mast extrusion (or entire mast) from dealer, they will be able to get you the right replacement. It will cost $700 or more, I guess.
If you are going to replace the N5.0 mast with mast from another boat : any NACRA mast or mast extrusion should do, since the 5.0 is (was?) the shortest, and probably the thinnest, wall extrusion of all the NACRAs. Some trimming to length may be required, and to do this, you may need some good measurements from an actual 5.0 mast - e.g. dist from top to forestay connection, upper diamonds, spreader, lower diamonds, etc.
When I lost a 5.0 mast, I replaced it with a 5.7 mast extrusion, and it worked very well. I also upgraded to adjustable rake spreader, instead of old-style through bar spreader.
The other answers were correct, make sure the mast is rigged with diamond wires, the 5.0 definitely needs diamond wires.
Good luck in the auction and the rebuilding. My N5.0 was bought in a credit union auction, and gave me several years of sailing pleasure before I sold it for parts. It is still "sailing", in Frankenstein-like fashion, in various pieces, as parts of many other boats.

I still have some NACRA mast parts, actually for N5.0. If you end up building a mast from extrusion, maybe these parts will help.