In the USA beef marbling is graded by the USDA - and this grade labeling is enforced to be passed nearly to the end consumer (i.e. the labeling is on the cryovac). So if I wanted well marbled beef in the USA, I could either buy in cryovac, comparing unit prices between prime grade and premium select grade, or in the grocery store where the cryovac is opened, I can see the marbling myself and make a judgement.
I am living in the UK, and although we technically have access to EU beef and a number of non EU imports, most available beef is UK sourced. And most consumer education is around awareness of beef cuts, food safety and animal welfare, rather than any information about beef quality.
When I approach butchers at say, Smithfield Market, they conflate quality with country of origin, following I think the attitudes of shoppers here (UK citizens seem to think if the meat comes from a faraway country it will be swapped for horse meat).
Finally I find that in the UK we do have carcass grading - to identify females or age of the animal. But as far as I can tell this information is unavailable to the end consumer.
So if I don't care a whit about country of origin, and would simply like the most well marbled best tasting product for my budget... how to shop?
Since meat is heavy, I prefer to make my purchases online.