Where can you buy Captain Underpants and the terrifying return of Tippy Tinkletrousers?

it is still coming out with the new books:captain underpants and the brainy bamboozle of the black cheetah man,super diaper baby 2,captain underpants cartoon o rama(drawing),frankenfart vs. the bionic barf bunnies from diarhea land,captain underpants extra crunchy big crunchy book o fun(not sure of the name)see them in the 8th book (preposerous plight of the purple potty people)except for the brainy bamboozle of the cheetah man