It appears that the Gardners are back in business, under the name of GOG Paintball. They are continuing to supply some of their cheaper markers, but no sign of the Shocker yet, and of course, the Nerve was already out of production anyway. I think 2006 was the last year of production, but don't quote me on that one.
It's possible that they may have some Nerve parts available, but I couldn't comment on that.
Some Shocker parts will fit the Nerve, and some Nerve specific parts are still to be found in shops, both stock and aftermarket.
is generally a good first stop when looking for any Smart Parts items. www.smartpartsparts.com
is another one.