I have seen genaric 4 lug spacers. The pictured set I found at the siteI'm not a fan of shimming out wheels, but it's not a driver, so I'm going to make a full spacer out of aluminum when I get back to work (unless someone knows where one could get a wheel spacer for 4-lug Falcons).
below. I'm not sure they woudl meet your standards but @ $10/pr. they would work until you get around to making a custom set.
http://www.ezaccessory.com/
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