Apparently there's no legit epub version of
Stone of Tears available. (Amazon does have a Kindle version, which means you'd have to strip the DRM and convert it to epub format for your Nook.)
Re using a library: You can check out books from any library for which you have a library card. You can go to your library's Web site and see which ebooks are available; sadly, many libraries have only a limited selection.
Some libraries will allow nonresidents to obtain library cards for a yearly fee.
Free Library of Philadelphia is one such; the card now costs $35.