Walmart, Kmart, any boat store (west marine, boaters world etc), will have those. The first time you fill it, buy the Pennzoil with the pump, solely so you get the pump. The rest of the time, just go with whatever is cheapest, provided it meets the requirements of API GL-5.
People will always say the same thing that is said about 2 stroke oils - must use manufactures brand. However, that is not needed. On 2 stroke oil, the lubrication is EXACTLY the same between say Pennzoil, Supertech and Yamalube. So, lubrication wise, you would be fine running Supertech in a Yamaha or a new Merc. However, Yamalube, and Evinrude oil and such have their own additives, and many are synthetic. So, while they lubricate better, the difference is in how they burn. But, for gear lube, you aren't burning it, so any brand will work, as the lubrication aspects are identical across the board.
