If you have a projector of any type, you will need a projector screen. Most screens you can buy will come with a mount. Once you decide what kind of mount you want, your next step is finding it.
Call your screen's manufacturer. If you already have a screen, the manufacturer will have the best suggestions for mounts that are compatible. The manufacturer can also direct you to a local store where you can buy it.
Step2
Check your local office supply store. Remember that an office supply store will carry only a few different types of projector screen mounts. You will have the best luck if you go to the same store that sold you the projector screen.
Step3
Try an online search. There are hundreds of specialty online stores that carry only audio-visual equipment. Find a store that specializes in audio-visual equipment. This store will give you the opportunity find and compare several projector screen mounts at once.
Step4
Search through local listings. You might be able to buy a used screen mount from a local business. Check listings in your local paper or craigslist site. These are good places to find second-hand items, and they may have the mount you're looking for!
Tips & Warnings
Many screens are sold with mounts. If you already have a screen, make sure that the mount you choose does not come with a screen. Unless, of course, you want an extra screen.