You mean the actual gears or the two speed tranny? Either way, yes they do sell them parted out and built. You might want to check with your LHS for the actual part numbers and pricing. I will try and dig them out and post them here.
Here's a search result from Tower Hobbies. You may find what you are looking for on this page or the ones that follow it (there are 88 parts listings).
Then I suggest asking your LHS if they carry that promotional part. Otherwise, you will be looking through the parts I posted from Tower Hobbies or another online HS.