I've only seen custom cages on the stunter bikes. Unless you are going to go for a street fighter you will probably have to really modify the fairing to make one fit. I'll see if I can find a link for you.
They do make engine bars in Europe for the GPZ500S (overseas version of the Ninja 500R). You can find them here. But they don't have a picture up for them. Here's a picture of the similar bars on the naked version of the EX500, called the ER5. You find them at the same site:
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