You can download the style you want from the endnote website. The program only includes the most popular styles but the website has a wider collection of styles. Please check out this video which explains the process in details:
in here on the page 46 you will find the instruction how to do it, however I would recommend you to find the style similar to what you need and change it as you want (described on the page 55) http://endnote.com/sites/en/files/m/pdf/en-x7-win-editing-reference-types-styles.pdf