You can really get some word of mouth by targeting individual communities that have a huge (but under served use case) - and writing out if ten box integrations for your service so that a power user or low level admin can install your plugin.
Two communities that might be interested:
Educational/LMS (specifically moodle, open source educational Learning Management System) - the web LMSes don't target printing of tests, just online testing. Quite a few teachers want to print out tests and have been using some serious kludges like moodle2word that involve having specific versions of word, installing templates, etc. This would be a godsend.
CMS and or Bloggers (ready to go wordpress (put shortcodes in a page), django, etc integrations) - lots of CMS data is dying for printouts...but there aren't any flexible printing services that allow for a customizable template — all I've found are glorified browser print buttons.
ERP also seems like a natural fit.
Anyways, it seems like you need to reach out to individual communites and try to work with them directly via their plugin repo's to get the ball rolling.