
I believe Pets at Home only stock calcium with added phosphorous. They used to stock bone meal - but it was horrible stuff and potentially dangerous. I bought it once and the container (Walfcol I believe) was full of dry, sterilized (cooked) small shards of pointy bone. If you can find human grade powdered bone meal at a health store; that would be fine.
Holland and Barrett stock a chewable calcium tablet - all it is is calcium carbonate. Just make sure to look for one with nothing else added to it, wherever you buy it.
If you like eggs, you can also save the shells, grind them to a powder - a teaspoon equals 1,800 milligrams of calcium.
From my notes:
Calcium/Phosphorous Ratio needs to be 1:1 (minimum) to 2:1, which equates to about:
800 - 1000 mg calcium per .5 kilograms
I'd recommend you get a good book on nutrition, I like Pitcairn's Natural Health for Dogs and Cats. Probably anything by him would be fine. He gives recipes and although he recommends raw, he also says you can cook the meat. (I don't feed raw.)