For red-fleshed apple varieties, you might try contacting Hocking Hills Orchard. They have an extensive collection of red-fleshed apple varieties:
http://www.fourseasonscabinrental.com/redfleshedapples.htmlI have a few.
Niedzwetzkyana - the original species, totally dark red
PI629319 - beautiful gray/silvery foliage and a red-fleshed apple. No name, just an accession number, from a botanical collection in Kazakhstan
Unfortunate thing about red-fleshed apples is that most of them are very susceptible to apple scab, a trait which they inherit from Niedzwetskyana. The recent commercial releases of red-fleshed apples are the result of a breeding program to try to improve this trait. The well-known crabapple Prairie Fire was also a result of improving the scab-resistance by breeding with the totally scab-resistant Japanese crabapple, Malus floribunda I think.
I just started growing Odysso and Calypso from OneGreenWorld.com that come from the RedLove breeding program.
Burnt Ridge Nursery had one of the Etter apples, Wickson crab. I've been interested in it, but never tried growing it.
Edit: Burnt Ridge doesn't list Wickson on their web site now, but Trees of Antiquity offers it:
https://www.treesofantiquity.com/products/wickson-apple-treeI have a few other rare apple varieties from a botanical expedition to Kazakhstan that are not red-fleshed. I did not know what the fruit would be like when I ordered the scions from Nick Botner's scionwood orchard, before he retired. However, I wanted to have a sampling of the genetic diversity of apples from Kazakhstan for possible apple breeding.