The closet frame from not customizing would be 27x40 and plenty places carry it. You can either center it with some space on the sides or you can offset it and put wording about the puzzle on the larger space.
Call Michael's, they may be able to order a frame that size if they don't have it in stock.
Custom framing is rediculous expensive but use a larger frame and outta background border for lots cheaper.. I've done it
You can shop the Michael's web site for sizes. They do custom frame work for hard to find sizes.
You are asking this question to the general internet community for the correct answer to the question you should contact the store directly
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