The wheels you have are obviously not OEM. I suspect they are Pantera East or perhaps Wilkinson wheels. If a tire set is not available via Tire Rack or On-Line Tires then stack your 16 inch and 17 inch wheels in the garage and opt for a more modern tire set in sizes that will be available for a while.
We can't help with a wide range of custom sizes, but as a club we do our best to guide owners towards modern sizes that will best replace the OEM tires. Maybe this little chart we've put together will help … maybe not. But we exist to help you one way or the other. Debbie and I guarantee nobody has put more effort into this subject than we have.