You will want to take measurements of the outside of the driver. I assume you want a speaker that will sit in place of the old one.

Both Parts Express and Madisound have a big selection of speakers. If you contact either of them, I am sure they can help you find a suitable substitute. It is more than just getting the same size driver. To sound best and to work well with the crossover in those speakers you will want to select something with similar efficiency and Thiele small parameters as the Philips or it won’t sound right. I am struggling to find a data sheet on them. Either of them might have some experience with these and may know what works best. You could also try a DIY message board or possibly the forum at Audiogon.

There is something to be said for the NOS driver in that nothing will integrate as cleanly.