I have a vague recollection that many moons ago the early DB2 docs contained real EBNF diagrams. I would not be at all surprised if somewhere in IBM there is tool (that the author is no doubt very proud of :), that takes EBNF syntax as input and produces these diagrams as output.
It just might be worth contacting your local friendly IBM support person and asking if there is any chance of tracking the EBNF down.
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