To be honest mate i would avoid ebay for badges theres no garantee on genuine ones if there any. You should always avoid cheap copys or replicas as they are not as strong as the original and dont have a strong spring back motion. Although at the local dealers it may cost a bit more its worth it because you know its genunie and will garantee fit if you quote your chasis number when going there.
PS. bonnet badges NEVER snap off unless theve been snapped off by a vandal OR if there fake/copy badges!
I had mine snapped off by some prat, so rather than replace it with another I just bought a flat cap which is slightly more expensive but it stops you needing to replace the bonnet star when it gets broken off.
I don't know a part number but if you ask at the stealer for whichever badge you want whether its a replacement star or flat badge they'll just give it to you.