If I had a set of gage blocks, I would use them as my local primary standard. Unfortunately, I don't.
I check my mikes and calipers against each other, figuring that it is highly unlikely that two measurement instruments would go out of calibration by the same amount so if they both read the same, they are most likely good. It's making some assumptions but that's what I have.
This is a hobby for me. I do very little work that would affect the outside world and what little I do isn't that critical in terms of tolerances. Any machining that I do using either the Tormach CNC or the DRO's on my lathe and mill drill agrees with my endearment instruments so I am happy.
Here is an idea though. I think it could be nice if we had a travelling set of gage blocks, ring gages, pin gages, etc. which could be loaned out to HM members so they could calibrate their metrology tools. A tutorial thread could be posted to teach people how to properly run a calibration. There could be a nominal charge to cover shipping and calibration costs. A reduced charge could be used as an incentive to become a premium supporter.