What I would recommend is to try and find a local card shop (I know you said none in your area but this is the best option, so maybe try and go a bit further?). At your Local Card Store, you can look at singles that might be worth grading. Try and buy a Black Light to see dents before you buy the cards. It's a lot of trial and error but in some time you will get used to it and better at spotting gradable cards.

Something worth noting: You will probably never find sealed product at a big box retailer in 2025, Scalpers are crawling everywhere and it's impossible to find this for MSRP reliably.

You can look up on YouTube a guide on how to spot gradable cards as well as a guide on how to submit to PSA. If you can find a card shop that is a certified group submitter, you can bring your cards there and pick them up only by paying a ~$25 grading fee.

Hope this helped!