Get an old used cheap bicycle. cut off the front fork and tubing, remove the tire from the back wheel, put the back wheel on backwards so the chain is on the opposite side. Change the pedals and sprocket to the opposite side. Mount an 8 inch or so stone to the adjustable seat post with a shaft and a couple of bearings and a V pulley. Put a thin V-Belt to power it around the back wheel sans tire. Make a mount to get the thing up off the floor so the wheel and pedals clear. Set on a chair or stool and pedal the thing to turn the stone at whatever speed you want.

Make a big wheel out of wood and glue sandpaper cloth to it like the old stones they used to employ for sharpening. Doesn't take much pedal speed to move the bigger wheel at a pretty fast clip.

eBay: PRIMITIVE

I do believe this is what you are refering to. I found it on the neo-tribal metalsmith's website. Scroll down to the bottom of the page.
Link

Hey all,
If anyone is in the kansas area, or knows of someone in the kansas area, you might want to snatch that pedal grinder up. Other than the stone not fitting the axle (which i think could be fixed with some creative concrete/mortar work...) that thing is beautiful. I've seen one go for $75.00 at auction once, without a seat, and with maybe twelve inches of stone left. With that much stone left that is one heck of a deal IMHO.

Here's a 24" dia. x 6" wide diamond wheel I put to use with a shop engineered stand and pedal a couple of years ago. Works great!