I am looking for a narrow bookcase for pocket books. Maximum outside
dimensions 5x36x90 inches. Where can I find that? If it does not exist
what is the closest dimensions?

Maybe a storage case for CDs  or DVDs

Hi hyppolite,

Well, I know they exist because we have two, but it will be hard to
find any so tall (perhaps you can buy two and stack them).

Paperback Bookshelves:
http://www.multimediashelves.com/paperback-solid-wood-bookcases.html

"I build my bookcases tall, narrow, and just deep enough to hold many
books in a small amount of wall space.  An eight-foot high, two-foot
wide bookcase for paperback books will typically have ten 5-1/2 inch
deep shelves spaced 7-1/2 inches apart to hold close to twen­ty feet
of books (roughly 250 paperbacks)"
http://www.wsfa.org/journal/j99/6/

Happy booking,
hummer