You can purchase comics from CBI! Tap on "Shop for Missing Issues" shopping is done through eBay so you will need an eBay account to actually make a purchase. Please read the disclaimer... You are responsible for any auctions that you win.
Select the title you want to shop for and press search. The list of titles is built from the comic books you have loaded, so you will need to load at least one comic book before you can shop for more.
View the list of items on sale right now at eBay.