The easiest way to make alphabet flashcards is to write the alphabet on 3x5 index cards. First, draw the letters in pencil (Aa, Bb, Cc, etc.) onto each card. Then trace and color in with dark colored markers.
Another way to make your own alphabet cards is to type the alphabet in Word in a large font. Print off, cut out letters, and then tape or glue them onto index cards.
There are also free online alphabet flashcards you can print off:
Animal ABC's Ring Flash Cards
Alphabet Flash Cards (Brighter Child Flash Cards)
Kids Preferred A-Z Smarty Kids Cards