How about a 26" wide Ampeg 810? I don't think 1/2" on each would be too noticeable.
Otherwise there are several old Peavey cabs will be 26 inches or wider, at least one of their older 215's and of course that big 28" wide Peavey 412 TVX would certainly be wide enough.
Anyway, found this thread, it may help: Recommend some "fridge" width cabs
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