get them from a thrift store, try to find the oldest one you can, the ones from the early 20th century are SIGNIFICANTLY better than modern examples.
the pot-iron they make modern pans out of are nearly-impossible to get slick, the new ones are much thicker and heavier but also much more brittle.
I have a hundred year old Wapak I use every single day and I consider it a blessing from God.

Other great brands are BSR (although their stuff will always be unmarked), Griswold, and Wagner.

They started adding the 'Made in USA' stamp in the mid 60s, if you find with without a Made in USA stamp it's therefore earlier. The more crude the logo looks the earlier it is.

If you find one, the only thing you should do to 'test' it's quality is confirm the bottom is flat by putting it on a flat surface like a tile floor and seeing if it spins, if it doesn't spin (and sometimes even if they do) buy it.
It doesn't matter if it's covered in rust, 100% of dilapidated cast iron can be easily restored, you literally just wire brush the rust off and slather it with oil and bake it to season them.

They are god-tier cookware. Op is probably a spamming bot but they're incredibly good.

picrel is the same as my beauty