Try Lucas Tires or Coker Tires online for Vredestein, Michelin XZX & XAS or Google for the size, & you may come up with a few others sold by Discount Tires etc. (usually Bridgestone &/or off brands & T rated - which is between the 1.7/1,8L S & the 2.0L's H rated, T wasn't around back then).
165R15 choices are pretty slim!
In the Originality & Hostory section is a lot of info on these OE size tires.
If cost is an issue, the Porsche factory recommended 195/65HR15 as the next best "modern" tire option, & there are a bunch of those available from the cheaper sources in name brands & others.