The Flowtec copies aren't being made any more. The guy that used to make them also makes the knock-off Mantzel Powerbox style intakes which are used on the Corsa B GSi C16/X16 engines.
Also, from various sources on the interwebz, the dBilas manifold is a massive waste of money, particularly on a standard engine. If you're turbocharging the Z18, then the manifold starts to become worth it.