here are some steps that will help to get deep internal pages indexed:
1) Make sure it has significant unique content.
Search engines may visit but tend not to index low quality pages.
2) Increase Google toolbar usage
Google likes to discover pages based on user activity. If your page is great then simply publicize it and get people with Google toolbar to spend time on that page.
3) Boost unique internal linking
Add links from your other pages to the internal page. I am not talking about adding to the footer, I am talking about adding unqiue links embedded in relevant content.
4) Submit sitemap
It does not hurt to submit a sitemap with all of your pages. It also does not guarantee all of your pages will be indexed. Its easy to do, so why not.
5) Boost external links
Develop links from relevant external websites to your deep content. It is ideal to gain links from external websites that are likely to generate traffic.
ps please remember that almost every website will have some webpages that just never get indexed. this is because almost every website has some very low quality pages that dont need to be indexed. search engines are not looking to index pages that do not add value to their serps.