I've pretty much run out of standard Shakespeare plays and epic poems to turn into three-panel plays, but fortunately there's still a lot of kinda-sorta Shakespeare material out there! Let's take a look at the anonymously-published Edward III, which is now generally accepted to have been at least partially written by Shakespeare:
OK, so I (a) haven't read Edward III, and (b) haven't read any of the scholarship surrounding Edward III, so I can't tell you anymore about which bits may or may not have been written by Shakespeare. As a huuuuge history play geek, however, I would absolutely love to see this at some point, as it serves as a very nice prequel to Richard II.
Edward III geeks out there (and you know who you are), feel free to geek about Edward III in the comments. If you have any easily-digestible reading material on Edward III to recommend, do share!