There's two other ebook stores I've used with my Kobo.
Google eBookstore,
http://books.google.com/ebooks , sells books in the Adobe DRM format which you can download to your computer and then USB transfer to the Kobo via Adobe Digital Editions.
And the same with Books On Board,
http://www.booksonboard.com . Books on Board sells physical books as well as ebooks in different formats including the Adobe DRM ePub format that you can use on your Kobo. Use Adobe Digital Editions to transfer the ePub from your computer to the Kobo via USB.