I know you are looking for different sizes, but I wanted the standard
165R15 for my 68', and I had a hard time finding them. It seems the main manufacturer of these tires (at this point) is "Kumho". They are officially on National Backorder, and likely they will not be making any more of them.
I was able to track down some pretty old threads on this group (from
2003) on the topic of 165R15 tires shortages and I found most people found their tires at Sears.
So I went on over to Sears an hour or so ago, and ordered a set for $43.99 per tire. Of course, they had to be ordered, but I can wait a couple of days to get them. They had cheaper tires (down around $34) but they were all long since discontinued.
Anyhow, for the standard sizes, Sears is still the place. :-)
-Ray