Hi,
you can get all related paints for the year and make at
http://www.motorbikepaint.co.uk/. Quite pricey but they do good matches.
Cracked temp gauges seem to be a perennial problem on 9**/748s, must be a stress point or something. It's a sealed unit so you would have to cut the old lens off and plastic-weld a new one on. Easier to buy one on Ebay (or live with it!).