Ruth, That should be simple enough to make up yourself. Chain the lenght of the swifter base. I would single crochet untill your piece wraps around the base.(using a cotton yarn) fold it over the base. make sure it is snug. I would then stitch up the short ends on each side. Add some string to tie. That should work.
Kathy H Farmgirl Sister #81 "To the world you may be one person, but to one person you may be the world..." (anomymous)
I use knitted and crocheted dish cloths (that have seen better days!) with my swiffer. Just poke the corners of the cloth in the little holes on top of the mop head. Works great for me.