The throttle inner comes with the grip as a complete unit. Available at www.cmsnl.com for 21.50euro plus postage. I had a quick glance and it seems to be the same part no. ( 53140MY5860 ) for all years, but to be sure Click Here and select the year and country for your m/c and then scroll down the page to 'SWITCH/CABLE' section.
It is also available in Fowlers and Lings but more pennies.