The plugs are available from porsche. You can check out the part numbers on the porsche maintained parts manual in pdf form. To get them out is a bit tricky. One that have direct access from behind can be driven out. Others would require one to drill and tapp the plug to be (small) slide hammered out. New ones can be installed using Loctite 574. Ones that a cup like, can be drilled and pried out, be careful not to hit the sealing surface. Those can be sealed with JB Weld on the sealing surface going in and the top sealed with same.
Catalog:
https://www.porsche.com/usa/accessoriesandservices/classic/genuineparts/originalpartscatalogue/