You should search the Internets a bit more: there are definitely good "how to" guides online.
Pigs always have been about a buck a pound for IBP "factory" pigs at Peoria, Grant Park and other Fulton packers. Little or no lead time to get a 100# or more pig at Peoria, eg.
If you want a "designer" pig -- by breed, farming methods, etc. pig, Gunthorp would probably deliver you one. Great folks, great meat. Several others have been discussed here and some are mentioned in the threads Cathy linked. Much more expensive, but also much better tasting.
Banana leaves are in every Viet grocery store in/around Argyle and at various Filipino stores such as Uni Mart. They tend to be much more expenive at Latin groceries for no good reason.
Banana leaves impart some flavor, make great serving platters, but don't play a huge role in holding in the heat/steaming. That's done with lots of wet burlap, then dirt/sand. I have done this using regular soil and don't think it makes a huge difference if the the pig is deep enough. The clay soil here might retain heat as well as sand. Don't know. If you want sand, it's cheap. Get some at Home Depo or have some trucked in.
Roasting a whole hog is 70% logistics and paying attention (the rest is experience and skill that comes with practice

) . Make sure you have everything you need, including a large patch of earth that will never be used to plant anything ever again (the lard and ash are caustic and kill the ground) and that the pig goes in with enough embers/hot rocks to get the job done. If he's not cooked when you dig him up, that's it for the pig roast. Also, make sure it's well secured in chicken wire. It's like jello when done.