Logitech sells them but it seems only by individual sizes (5 pairs for $10 + tax/shipping).
I'm thinking they may only be worth trying if you prefer the sound with tips with wider bores (like the stock tips) AND if the stock tips don't fit all that well in your ears. The stock tips work for the most part for me, but I think my ideal fit would be a size in between the medium and large sizes because the large is a bit too big for my preferred insertion depth and the medium has a tendency to lose its seal if I open my mouth wide or lie down with the IEMs in. I have no such issues with the TF10 tips.
For people with larger ear canals, the fat tips that come with newer RE-400 (and RE-600 I believe) might work wonders (while also maintaining a wide bore for all sound holes to be unrestricted). Unfortunately, they're more square shape than even the stock tips, so people like Dsnuts may be out of luck.
They're the clear ones on the right in the pictures below. For reference, the grayish ones on the left are the largest size UE900 tips, and the middle black ones are the largest stock tips.
Edited by PeterDLai - 8/30/13 at 10:07pm