THE VMR V810 are offered in a 18" size.
http://www.velocitymotoring.com/wheels/v810/
You also have the OZ "HLT" models, some BBS options like the CH and CH-R, and a several options from Enkei. I think some of the Advanti wheels are, and I'm sure I missed a few....
To add to that, all "Flow-formed" wheels are some type of cast wheel. Just the barrel is rolled or formed to make it stronger, and require less material.
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