Hi Ginta and welcome,
If you want to work for an agency first I'm afraid there aren't many that cater for BBWs. They don't know how to market us. I don't know where you're based but there is one agency who specialises soley in having BBWs on their books. They're called Curves Unlimited. But you have to be English. I'm not quite sure what that means exactly, it's open to interpretation. But you could give them a call and ask.

Otherwise, speaking from experience, I would go independent. Read the main site of Saafe, especially our 10 point guide to starting: http://www.saafe.info/10point.htm . Use the search facility on this forum found in the top right-hand corner. There's plenty of advice given on starting up.
Good luck.

Thank you for the reply.

What is wrong with agencies? Why they cannot market BBW girls?

BBWs are a niche market. It's a speciality. Some agencies and the people who run them don't know how to market BBWs. And not just that, they just don't want to either. They don't think there's a market out there, or at least enough of a market to warrant taking up space on their website.
It's as simple as that really. That's why we're better off on our own. We know how to market ourselves to our best advantage.