I was looking for the same a while back - didn't get very far to be honest (though the eBay link above looks not too bad, and hadn't seen that before). Other than that, the best options were either bigger multi-filter holders, or improvised solutions - sunglasses cases (just microfibre cloth with a drawstring end) can be found on eBay really cheap, but obviously they're about twice as long as they need to be. Otherwise i got sme microfibre lens cloths which i intended to sew into little pouches, but not got very far with that either!
Sorry, probably not much help, but there just don't seem to be any out there.
David