16" is all you'll find. No 17" steelies out there that I've seen or heard.
Mine has 16.5's as well, just bought tires a couple years ago, not too hard to find,,,,,yet.
I honestly don't think they will completely go away, but I would assume in another 10 years tires for the 16.5's may be very expensive. Some of the vintage tire makers may also pick these up, never know...
For specialty wheels I've always used Wheel Vintiques. I'm sure they could come up with what you need, just gotta pay
