make them yourself?
I would pick the fabrics I wanted, and then iron them onto some heat bond or other double sided fusible interfacing. Print or draw the letters you want onto paper, and cut them out. Place on the paper side of your interfacing upside down and trace. Cut out the letters, peel off the paper, and iron onto your item. Satin stitch or zig zag around the letters.
I used to make my own appliques, so that's what I would do...sorry if that's no help, though!