If you find somewhere, please let me know.
He (MCQ) got his from Axminster tools, but with postage it comes out expensive, and I couldn't justify buying extra stuff just to save on postage. In the end I bought a 500g bar of Silverline blue honing compound off eBay. Used it a couple of days ago on a leather strop and it works a treat, although I can't compare it with real Smurf Poo as I've never tried it.