I have an ancient Kurta that works really well. It has both a pen(plugs into a serial-port like connection on the back) and more complicated cursor-type tool.
It was given to me, so I'm not inclined to sell it(plus I do use it on occasion). It would also probably be prohibitively expensive to ship across the pond-it's a heavy beast, and would take a lot of packing to make sure it arrived safely.
I'm posting primarily, though, to just mention the brand and say that I've had good luck with in everything from System 6 to OS 9.
All of that said, USB support is actually pretty good in OS 9, as by the time OS 9 came out every computer Apple was selling was USB based. OS 9 was released in October 1999, and the last computer with an ADB port(the B&W G3-which had it for legacy support although it was primarily USB) was discontinued in August of that year. I can't give any specific advice, but if you do buy a USB based pad try to find one made in roughly the 1998-2002 ballpark and be sure OS 9 drivers exist for it(they probably do if it was made during that time, although it may take some digging to find them).
I can understand your desire of an ADB tablet, though. My Kurta "just works" on every computer where it's been connected.