www.greekclothing.com if you sign up for their mailing list,they send discount coupons every week or so. if you want the satin stitch, make sure the product page says "double satin stitch" otherwise its just the not so nice kind. good deals on packages.
www.designergreek.com a little pricy, but you can customize all kinds, and even specify double satin stitch on just about anything. they also have a design center, where you can pick your letters, and the colors of the garment, and the colors of the letters, to see what it might actually look like.