Hit up forum members "azwelke" or "David Brown". They have created some awesome kydex sheaths. I have personal experiences with both and they both do great work. Fast, reliable, fair price, etc. I don't know if either of them has a Spyderco Mule (they both tend to hang out on the Busse forum), but contacting them couldn't hurt. Worst case scenario, you may have to send them your knife for a day or two. It's worth a shot to me.