Thanks where would you go to buy a movie poster frame or have it done ?
You have several options.
You could use a neighborhood frame shop and have them create a custom frame using your hand selected pieces. This may end up being very expensive depending of the frame material, the matte and the glass (like non reflective UV or "museum" glass).
Another option is to buy a prefab frame at an arts & crafts chain retailer like Michael's or Aaron Brothers. You won't have the same range of choices or styles as compared to the neighborhood framing shop, but the end result may be acceptable for you. That's your call, of course.
Stores like Michael's typically have a framing department. They might not have the wide range of frames that a specialty frame store would have, but they might have something that appeals to you. Custom framing will definitely cost more than a prefab kit.
Or you could try an online retailer which is often the cheapest option. I've used
Poster Frame Depot before when I wanted a very basic prefab kit. There are plenty of online frame retailers, just use your favorite search engine.
So it comes down to a balance between budget and quality, just like in so many of life's purchase decisions. You're not going to get Aston Martin styling on a Honda budget.