Genki English has flashcard sets you can buy.
Who are they for? What age students?
Most kids text series have flashcard sets that match. You can get those from on-line book stores or contact a represenative to find a place that sells them.
Other than that I've only seen smaller 4x6 note card sized flashcards commercially. Most book stores that carry ESL textbooks will also have an ESL materials section.
Where are you? There must be some local importer that serves the international community there. I'm sure they have teaching materials in their catalogues. In Japan, the one I use is called the
Foreign Buyers Club
Last but not least, Amazon.
Amazon.com will ship over seas and I'm sure you can find something on there. The shipping cost isn't too bad for DVDs but flashcards might be a little heavy. See what they quote you. They're pretty fair.