i'm very late, but kpop usa (online) has a lot of stuff, and so do amazon and cokodive (online). walmart may have some, but mostly likely only the groups that are very popular overseas (eg., bts and blackpink, maybe enhypen or txt). if you have access to a target, they have a decent selection of albums. fye has albums, both in-store and online. you could also always go to the company website! they will have a shop for each group where you can find albums and other merch. hope this helps!
I used to mainly purchase them from ktown4u and kpoptown but then the shipping prices went up since covid, so I stopped buying them from those stores (except for one album where I bought from ktown4u in 2021 lol).
Now I buy them mainly from kpopalbums.com since their shipping prices are cheaper compared to the other online kpop album stores.