I had the same problem with my 83 SC, looking for 245/45/16 all weather tires.
No luck.
Was at Firestone with my daughters car and saw the size listed on the wall index.
PRIMEWELL PZ900, 40,000 mile, W speed rating, 94 load index. I never heard of them either! So, did some homework, bought a set and personally, quite/dry-wet performance, holds the curves and 20K later.................LIKE! Still searching but that size seems to be, like our cars, OLD.