Having a 10mm spacer is definitely a challenge for wheel vendors and spacers manufacturers alike. In fact anything between 8 and 13 is tough, because you are making a hubcentric spacer that has the same thickness as a hub. When wheels are machined with a high hub taper, stability and strength is sometimes compromised. I've also had a few factory wheels that were not compatible with H&R 10-12mm's.
We do have a couple of vendors who make compatible spacers for our wheels. If you are interested, let me know and I'll see if they can offer some sort of a deal for you
