I don't think that cartomizers come with a whistletip anywhere!
I make my own by using and 801 rubber whistletip I have from my penstyle 801 e-cig I put on top of the cartomizer. It works great because the rubber stretches enough to fit just right over the 808 and/ot Green Cig cartomizers.
Another thing you can do is take out the white topcap of the cartomizer before putting the whistletip on. Then it is really easy to refill the cartomizer from the top (808 only)