I had the same happen to me... but in my case I had the plastic cover to the battery power distribution box (also referred to as a fuse box) because I was curious on how to get the battery out (that was prior to actually looking at a YouTube video on replacing the battery). Anyhow, the terminal nut was corroded and the bolt snapped when I tried to remove it and, of course, the socket wrench fell right on one of the terminals in the box followed immediately by a nice spark and NSFW commentary by me.
Turns out it's actually pretty easy to replace. I could not find this replacement part at ANY auto parts store but did find it at some GM Parts Direct stores for anywhere from $56 to $75, but longer shipping times (unless you pay overnight shipping). Then I called one of our local Chevy dealers and they had the part in-stock for $86. Wife picked it up on her way home from work and I had the old one out and new one in in under 20 minutes - truck started up like a champ!
In my case (2014 Chevy Silverado 1500 WT) the description on the GM Parts Direct (and other, similar sites) was "Fuse Box - GM (84354716)". I gave that number to the parts department and they verified it was the right one for my truck. Even if your truck is different, they can probably use that as a guide to find the right part for yours.
WARNING - the part I got did not include the cover for the box as I thought it would. Luckily I saved mine - be sure to save yours as well as you don't want to leave that open to the elements.