No more TDK or Maxell being made, but plenty of it out there.
I agree TDK SA-X and Maxell XLIIS are the top choices, with TDK SA and Maxell XLII being close seconds and really more than adequate. From my early days of portastudio use starting with the
Tascam 144 I was a TDK man. Most of my early stuff is on SA and SA-X and sounds as good as the day it was recorded. All those early tapes were made in Japan, but I've found the later stuff made elsewhere to be just as good.
You can find them on eBay in spades, but don't pay too much! There is no cassette tape shortage to justify what some sellers are asking. There is plenty of new-old-stock sealed tape for the foreseeable future. $5.00 or more per tape is highway robbery $3.00 per tape is closer to fair, but if we were going by traditional supply and demand then $2.00 per tape is more like it. Just don't get ripped off! Prices vary greatly among sellers. Also pay attention to shipping and factor in total cost. A higher asking price but free shipping can obviously be a better deal.
60-minute length is best for performance and longevity, but 90-minute is not far behind. I've used plenty of 90 and 60 minute, but nothing longer because the tape gets too thin at longer lengths. Even if it doesn't break it will stretch and reduce the quality of the recording over time... especially multitracking with a lot of shuttling back and forth. So IMO make 90-minute your max.
You'll see sellers wanting more for older tape made in Japan. Skip that "Collectors Item" scene, unless you see a good deal and save some bucks. The Maxell assembled in Mexico is excellent. I've used a lot of it. The TDK made in Korea and the UK is also top notch stuff.
Set the search for USA only or wherever you are. Even shipping cost from Canada has made buying tape there a no go for me. It's more than doubled in the last few years.
Copy and past the following in the eBay search box.
(TDK, Maxell) (SA, SAX, SA-X, XL, XLII, XL-II, XLIIS, XLII-S)
Then change the sorting of results from "Best Match" to "Newly Listed" near top right.
You can also just google the tape types for other sources like Amazon, Craigslist, etc.