I sharpen my 6" on a diamond hone. Flatten the back, sharpen the edge, strop, and Bob's yer uncle.
Look up "Scary Sharp" and pretty much forget the coarser grades, under
100. I use 600 and 1200 diamond plates, plus a sheet of 1500 grit of wetordry paper, and a strop with Lee Valley green chromium dioxide crayon. I have to be careful waving my freshly sharpened tools around for fear of splitting atoms with the sharp edge. ;)
And if you find a copy of Leonard Lee's sharpening handbook, buy it. It's great, too.
Have never seen Shelton in any store, ad or online. Estate auctions, either. If it wasn't Stanley or Bailey(or Craftsman), it wasn't sold around my part of the country. I've been doing woodworking for at least 40 years now.
As far as sharpening, I'd use a fine diamond hone plate myself, if I needed a finer edge, I'd break out the Arkansas stones for finishing. If you had the planer attachment, probably the Delta wet stone grinder would work if you just had to have a power tool for sharpening. One of my really old books showed using something like one of those round axe-sharpening stones for sharpening a draw knive, this would have been for doing stuff like debarking logs for houses, though. As long as you get it sharp and don't get a turned edge doing it, just about any method will do.