I went through the Vex site but could not find this. Does Vex sell the metal (or even the plastic) inserts used in the 4" wheels and high strength gears?
We seem to be out right now at our club and I don’t really want to buy a whole slew of new wheels and high strength gear kits.
I don’t think so, but I wish they did. I also wish there were a couple of extras included with the gear kit so when a student opens the packet and they all end up on the floor we don’t have to find every last one.
I do not see that they sell them, but a high strength gear kit comes with 16 metal and 16 plastic, and with 8 plastic gears, leaving 16 extra inserts.
You need one metal insert each side of the gear, the plastic ones have a round hole, we rarely use those. So we have lots of extra plastic inserts and no metal ones.
whenever i use the high strength gears, i always use on metal and one plastic per gear - never had a problem … 
In our high stress areas we use 2 metal inserts to give the gear the most strength possible
A workaround is described here: http://botsnstuff.com/wiki/Gears#Gear_Inserts
My team bought like 4 packs of HS gears just for the inserts. (facepalm)