I ordered some from
www.clearbags.com They were good quality with a seal, and they were delivered quickly. My only advice is to order larger than I did if you decorate your envelopes, too. I ordered 5 3/4 x 4 1/2 because I mostly make 5 1/2 by 4 1/4 cards, but the envelopes didn't fit in. I hadn't thought of that when I ordered. It wouldn't make any difference if you just gave each card buyer a plain envelope, but if you want the envelope to fit, too, order a larger size.