Kobo only has book 6 of that series...
http://store.kobobooks.com/en-US/ebo...-and-tragedy-1
Amazon has all of them, but you'd have to convert them.
B&N has all of them, but buying from outside the US, although it can be done, takes jumping through some hoops IIRC. (B&N uses ePub, but if the books are DRM'd it's not compatible with Kobo and would need to be removed)...
http://www.barnesandnoble.com/w/the-...=2940013964679
http://www.barnesandnoble.com/w/thei...=2940014332125
http://www.barnesandnoble.com/w/the-...=2940013925465
http://www.barnesandnoble.com/w/the-...=2940013925496
http://www.barnesandnoble.com/w/clos...=2940013991989
http://www.barnesandnoble.com/w/triu...=2940014301404
Those are the only places they're available AFAIK. Otherwise as I said, contact Rosetta and see if/when they'll get the others up for sale on Kobo.