Advice on writing a letter to a business asking for something

I am an inventor and am trying to finish the designs on a virtual reality "POD" as I have named it. I barely have enough money to devolop a prototype using pvc pipe and the like and am in need of a VR headset to help with design and would like to know the best way to go about asking a specific company that manufactures them if they could supply me with one free of charge. Possibly one that works but has a defect or a returned unit or something similar. I am also wanting other information related to their product and feel that I should ask for that first so if they wouldn't be able to give me a headset they wouldn't skip over the rest of the letter and not send some other information. The VR headset is somewhat expensive so I'm not sure how they would feel about me requesting one. I have also followed their product since before it was release and feel that they make a far superior product compared to anything available (within that price range), which is why I am writing them.

Thank you,

Scott