Mickey thompson indy profile tires n50 14"

IDK about the N50-14 size.

As to 15" tires;
The N50-15 tire had a section width of 12.65" and an overall height of 27.50" on a 9" wide rim. The closest P-metric tire size would be a P325/50R-15. But Don't mount this on a 9" rim!
On the street you will need to run this at about 20>24psi to not prematurely run the centers off.
Ideally this 325 needs an 11 or 12" wheel which will add at least 1inch(25mm) to the section, making it a 350/13.8 section

The next closest is a 295/50-15,
but it needs at the least, a 10"rim, and I have had good wear, running them at 24psi.