Hi,
You can get entire packs including oil seals and gaskets, for both the gearbox and transfer box (separately).
There are various combinations of gearbox and transfer boxes so you would probably only get a kit for a gearbox and a separate one for the tranfer box (unless it is an lt95 which is a full combo box).
I think you can get them from most internet sites, paddock, craddock, ashcroft etc.
Just order the set for your particular gearbox and transfer box. i.e. LT77 , R380, LT95 etc and transfer box R320T etc,
you will (might)probably need the suffix (the letter at the end of the serial number), i.e. lt77 "f" cos some of the parts are different for different ages of gearbox.
Cheers
Stephen