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While looking up a map for a recent question I ran into Timemaps, which you might find interesting. It's interactive rather than a poster, and allows to zoom in and out of regions and countries, browse timelines forward and back, and read some details about what's going on. Example.
They're a commercial venture run by historians, and seem to target the teachers' market. They don't seem to offer any posters, but like any business they'll be on the lookout for potential sources of revenue that they haven't thought about. You might get lucky if you ask them to make one. (It seems, to me, that this ought to be a no brainer yes decision.)
Alternatively, googling "world history timeline" reveals a few existing options. Example.