Not sure where you'd go in NY, but when I needed some I just found an LBS that was a Cannondale dealer, and they had them. The plastic nubs have a plastic "expander nail" that you tap down with a tiny hammer (or sumthin') to make the nubs flare out inside the hole: sort of like a moly in drywall...if you get my drift.
Does anyone know of a source? NYC convenient would be a huge plus.
Danny, most C'dale dealers stock them. (at least around here)
If not, then go directly to C'dale, they should be able to help.
Tip on installing them...find a small diameter metal tube just slightly larger than those plastic pins. Then find a metal rod* that fits snugly into the tube.
*I used a short piece of steel welding rod. Comes in many diameters.
Now, place the metal tube over the pin on the guide and slide the metal rod into the top of the tube.
Tap carefully to install the guides pin.
If you just try to hammer the guides plastic pins, they will likely bend. and then it's a PITA to get it in after that.