Need to know why you think the starter needs to be shimed.
If it has shims now and you buy an OEM replacement starter, then use the shims. If it does not have shims then you will not need them. Replace the starter with an exactly duplicate, installed exactly as the original. If in doubt measure the distance from the mounting plate face to the end of the drive gear shaft and make sure that distance in the same on the replacement starter.
Do not install the shims. Your starter should work fine.
between the starter and what it is bolted to
One of the easiest starters ever... 1) Disconnect negative battery cable 2) Remove nut holding power wire to starter. 3)Remove smaller wire(s) to starter. Mark which goes where if several are present, and you don't think you'll remember how it goes. 4)Remove the starter bolts that are locatd directly under the starter. 5)Starter will come out of vehicle at this point. NOTE: Many Chevy's use shims to space the starter from the flywheel. If your vehicle uses them the new starter will likely come with shims. Use the same number of shims as was in the vehicle when you took it apart. If starter grinds when starting after starter replacement you may need to add additional shims.
disconnect neg battery cable. from underneath the vehicle,disconnect the solenoid wire and battery cable from the terminals on the starter solenoid. remove the 2 starter motor bolts and remove the starter note the location of of spacer shims if any are equiped. installation is reverse. and be sure to replace the starter shims in the same location between the engine and the starter if your model has one.
Check the backlash between the starter drive and the ring gear after installation. If it's too tight, use shims.
You should be able to buy starter shims at any auto parts outlet. If not their you could get them at the dealers parts department.
Disconnect battery. Then the electrical connection on the starter solenoid. Remove the starter bolts and the starter. Note the location of the spacer shims. Installation is the reverse. Don't forget the spacers shims or you will get noise when starting the vehicle.
There are several shims that could be used such as starter shims (for adjusting drive gear to ring gear), caster/camber shims (for front end alignment), body shims (for aligning body panels),
Disconnect battery. From underneath, disconnect the electrical wires from the starter solenoid. Remove starter bolts and the starter. Note the location of the spacer shims. Installation is the reverse of removal and make sure you replace the spacer shims so you wont have any screeching noise when starting. If you need more details, include the year and engine size of your camaro.
Shims bring the starter closer or further from the ring gear for proper alignment.
No, you should get new shims from wherever you got the new starter, but if not, make sure they go back into the same position they where. New shims, make sure they are the same thickness as the old ones.