Try this vendor
on eBay. I've linked directly to the jars, but they sell lots of other items.
The jars are cheap, but pay close attention to the size, as they vary widely. I picked up a couple small ones from this vendor a year or two ago (before finally getting some much larger ones from overseas directly).
Also, as far as I know, long term storage of oolongs is best done in an air-tight container, and so a clay jar would not be ideal, if not detrimental.