Any cap that is the same size AND the same pressure rating, should work. IIRC there are different pressure ratings.
Caps often fail to seal because people have used anti-leak coolant, which typically has sodium silicate in it, which leaves a glassy mineral coating unevenly in places like the seat under the cap. Which then causes...a leak from the uneven seal.
Yet one more good reason not to use anti-leak unless you need it.
Odds are an old-time NAPA store would have a $10 cap that's perfectly good.