My favourite place to buy currency sleeves (& supplies) is at shows. I don't attend very many any more but when I do, I really like having the opportunity to discuss the type of sleeves (different brands) the dealer uses (or may recommend), + pages, binders, etc. I like to inspect them (just like I prefer to buy a catalogue in hand vs online). They're always priced well & it's nice to skip the added postage. I also like to take home something & often don't find banknotes at shows. (The same for a LCS that's nearby).