It is up to the venders themselfs, to provide banners, Most venders will have a page full of different sizes to pick from. But unlike banner networks where you link to their banners (i.e. you just place the code ) ,, at Clickbank you will mostly have to grab the banners yourself and add your AF code then up them to your site.
No clickbank does not provide banner ads. Clickbank only gives the text link to promote for each vendor. You have to request the vendor of the product you are promoting to provide banners if they are not available.
As the previous posters have said, CB only provides text links. To get other types of ads, you have to go to the affiliate section of the vendor's website.