Garry,
I don't see one on there now (not the set with Mr. Hankey), but make a eBay saved search for "South Park Figurine Set". IIRC one set contains the figurines for the 4 kids, and the other has Chef, Mr. Hankey, Ike, and the cop. I've got a set of each in case I ever feel like or need to replace the playfield toys on mine, so I can confirm they are the same thing.
If you buy the set that method it will cost about $10-20. If you search for "Mr. Hankey pinball" something or other it will usually be marked up by a pinball retailer and cost a lot more.
Same thing applies to the Kenny playfield toy, Cartman topper, and - if desired - toppers of the other kids. I forget what those were packaged as though, think it was "South Park Collectable Figure".