Is there an easy way to build deep links from other sites?
You need content that people want to deep link to. You were part way there with your resource pages. As I said before identify a classification of your content and create a resource page for each classification. Then look for specialist links for those classifications. Details would depend on the nature of the site and content but for "costume" I would expect there to be specialist niche sites around that would happily deep link to a relevant page.
Link building is more than a mathematical exercise to game the search engines. Real links from interested sites will bring traffic in their own right. A quick and unscientific eyeballing of recent hits on one of my sites showed about a third of the traffic being from links rather than bookmarking or search engines.