Everyday Language Learner wrote about Using Paper Flashcards but with spaced repetition.
My favorite is Tuttle’s flashcards for kids.
Other flashcards made to educate children I repurpose for reviewing basic concepts in Korean like numbers, telling time, colors.
Get creative. I make my own flashcards from found items. For example, I have Twilight flashcards now when I turned some expired coupons into flashcards. Decks of playing cards make a nice size for flashcards, just put a sticker on one side and write your own. Jumbo craft popsicle sticks, jenga blocks, colored paper, puzzle pieces, ABC blocks, scrabble pieces, etc. can be used.
I have a very cool deck of 50 Zen cards which are now being used to memorize the Zen words in Korean.
Like to garden? Use the backs of old seed packets to learn the words for your flowers and vegetables. Have a hobby? Cut up pictures from a magazine to make your own personalized cards. Use your imagination.