There are no officially released complete sets of the Studio Ghibli films. There are some sets though that you can get, which are official:
Japanese Takahata films
Japanese Miyazaki films
North American Miyazaki films Canada
North American Miyazaki films US

I find the best place to purchase the movies is though Amazon though. They have them all, and since Amazon almost always lowers their prices to match competitors, it tends to be the best price. At the moment, Amazon Canada is matching Walmart, so all the Ghibli films are $19.96.