Silver Lake has two shops right at the entrance that stock the most common parts and what they dont have they will get next day for you.
a little more about SL.. to ride the dunes your "supposed" to be 16.. but ive been riding there since i was 12. its pretty much ALL sand with one mud hole they allow you to ride in. theres lots of water holes to play in and a drag strip for some competition. theres a series of big hills to climb and lots of areas for jumps and other stuff. theres also an area with trees and trails going all through them, but its still sand, not like woods trail or anything, just a different play around area. if you cant bring a vehicle for the dunes they have rentals available- 4x4 quads, jeeps, mini sandrails
for overnight there are 4 or 5 campgrounds and quite a few motels to stay in
hope this helps to give an idea of what its like..