I've had two sets of spacer/adapters and can tell you a couple of good sources. First, if its a spacer or the common Honda swap, go to Ross at Modern Motorsports. It probably will be easier for you anyways as He's located in Vancouver. His were top quality and I ran them before switching bolt patterns.
For this stage of the Z, I am running a two piece, 4x114.3 to 5x114.3 adapter made by http://www.motorsport-tech.com/. Their service is very good, their spacers are insurred, come with new studs, etc.
Don't settle for the cheap fleabay parts. Its your wheel, and the difference in quality may be the difference between your wheel staying with your car or passing you in the other lane.
Just my .02
Cheers!
Bryan