In order to get a corporate sponsorship, one need to have a connection within a company. I'm not sure about others, but mainly for our team Parents and Mentors have helped a lot in bringing in the corporate sponsors. Most of them work for some really prestigious companies, and have links/connections within to spread the word. The main idea is to get the parents involved as much as you can, because most of them work in a company (small or big).
As 612 is located in the Technology Hub of USA, our mentors, teachers, and parents have connections within the companies or most of them work for one.
Not only that, over the years we've been able to get help/mentors from sponsors too. Some of them are Northrup Grumman, SAIC, Raytheon, Mitretek Systems, IEEE, Lockheed Martin, OEC, Fiserv, etc. (I know its shocking that all the rival defence companies are sponsoring a team jointly

)