These?
http://www.americanmuscle.com/1in-billet-aluminum-wheel-spacers.html
I really wouldn't worry about the tolerance and making your own... If you are too precise corrosion may end up making them stick on there. I'm not sure if you've ever had to hammer a wheel off a car before, it can be no fun. I've had newer 2011-2013 vehicles get the wheels stuck on them before. Even with a BFH, it took a lot of muscle to get them loose.
I really think you are worrying too much. There are a lot of good reviews of those spacers and you would probably hear about it if they were bad. People love to bitch more than they love to leave good ratings.