Items found in Black Rock City are not "playa gifts" to keep nor to give to anyone other than their rightful owners. At Burning Man, participants turn in found items to Playa Info so that they might be returned to their owners. After the event, whether you have lost or found something, there are some steps you can take to facilitate "happy reunions":
Send descriptions to lostfound(at)burningman(dot)com. Don't be vague or general in your descriptions: complete make, model, and color information will have the most success. Act quickly. Our official found items return efforts end when ticket sales begin in mid-January for our next Burning Man.
So--send them an email, as well as making an ePlaya post.
More tips are available here:
http://www.burningman.com/blackrockcity ... standfound
The best of luck to you.