If you have a grease gun (which is what you need to pump into a Bearing Buddy) then any normal tube of grease that you can get at AutoZone or other such place will suffice. You can get cheap stuff or more expensive stuff, but it's all going to work.
If you don't have a grease gun, go get one... you'll see the kind of grease tube you need to buy.
Additionally, most places carry Marine Grease in the same tubes.
For a full on thread on the best grease to use, check out: http://www.offshoreonly.com/forums/archive/index.php/t-78770.html