the 200's and 250's were available, but not widely. if you lived in a college town or a large town you probably could get them. otherwise, good luck. 20 years ago 120's were very common and 180's were one step up. when fitted sheets (yes - i am that old) were introduced, the thread counts went up to 180. that became the new norm. martha stewart has a bottom line for places like k-mart and a better line for places like, , say, macy's cellar. do you know the country of origin? when you say prints, you mean the old dye jobs, yes, they were gone. they were not replaced until those awful prints/patterns became available.
many people don't like the 300 thread count sheets. they feel flimsier, and they are lighter weight. thin strands don't weigh as much. they also have a body-feel that people are not used to.
someone asked where i learned this: my dh is an architect and he worked for rutgers university managing their in-house architectural department. we moved to this town because it was closer to his work, and bought a victorian fixer-upper. shortly after moving here and sinking a lot of money in the house, rutgers dropped their own department and farmed out that work. my husband was unemployed and my tailoring business had not yet taken off. i took a job at an upscale home furnishings store where manufactures made us take classes in sheets, pillows, draperies and such, so that we could knowledgeably sell. it was a fantastic education. we learned thread counts, different drapery styles, fancy drape rods, you name it. they spent a bundle teaching us what they felt we had to know to seel high-priced goods.
i've never looked, but can you google? i'm sure the library books has on the manufacture of household textiles.