What type of connector does the GROVE system use?
It looks like the Grove connector is proprietary. I emailed Seeedstudio, and they directed me to this datasheet. Unless I'm reading it incorrectly, it doesn't appear to correspond to any type of JST connector, although it's similar. It has 2mm pin spacing, which would make it closest to the JST-PH type, but all the other dimensions are slightly different.
Here is the updated link on the seed website.
Also note that Digikey now stocks seeedstudio stuff.
I believe this is the genuine article: Wire to Board connector > PITCH 2.00mm > 1125 Series
Good luck finding a vendor!