Can you still buy the sized Thirsties covers? I never used them myself but I heard that they ran bigger than the Duo wraps so the size large might still work for you. At this point I'd probably try to get one used unless you get it from one of those "try it and return it" online stores.
Bummis has a couple of options that come in XL like the basic pull-on cover, super whisper wrap and super snap. I'm sure there are plenty more, these are just the popular ones that came to mind.
Another one I thought of is the MotherEase covers. They give a fuller-coverage fit but both the snaps and aplix versions come in size large and extra large. I personally liked the snap ones better, they are quite pouffy on their own but smush down well under clothes.