I am staring a private clothing line and need to acquire a manufacture. How do I write the letter?

Do you have samples from your clothing line? Do you have a business plan? Have you sold any clothing yet? What sets your clothing line apart from any other clothing line?

Manufacturers will ask these and other questions. Your best thing to do is to visit several manufacturers in person and discuss this with them. That experience will give you ideas about your presentation. And you do want to see the manufacturer in person to see how well the factory is run, how clean it is, what other products does he make, etc.