Not sure an exact RAL code exists, although some suggest a match is RAL5002? Don't bank on it though. The official colour is Deep Purplish Blue Solid E (DPBSE).
If you're after aerosols, touch-up pens or larger volumes to spray then try
RS Bike Paints. I have always sourced my paint from them for British, Japanese and Italian bikes and they provide excellent products and service. They do Yamaha engine paint too.