Start by searching for sponsorship opportunities in your field of dance. Contact a sponsor that you know has sponsored other break dance crews in previous competitions.
Note down the names of advertisers at break dance competitions or other dance competitions to spot a potential sponsor. Contact all the advertising sponsors on your list via cold calling or e-mail initially to ask if they offer sponsorships to new crews, and if so, ask how to apply.
Visit retail stores that sell the type of clothes that break dancers wear. Ask to speak to the manager. Ask him if his company offers sponsorship opportunities to dancers who wear their gear. Be persistant. Explain why you need sponsorship and show proof of the competition. Be prepared to audition or provide a showreel. Sell your talent to the company in return for sponsorship, which would in turn help to raise the company's public image and maybe bring it more sales.
Search the Internet for sponsors. Check out arts and sports funding bodies that help support local talent. Check out websites that list sponsors and also allow you to list your crew as seeking a sponsor.
Approach a celebrity who shares your passion for break dancing via her agent. Send her a showreel and ask her to be your sponsor. Try approaching a celebrity who hasn't been in the public eye for a while and keen to raise her public profile in order to gain career oppotunities.
Check out the business telephone directory. Call every business you think would be an appropriate sponsor.