The shims aren't sold in diameter, they are sold by thickness, ranging from 2.40mm (0.0945") through 3.10mm (0.1220").The shim is identified by the number on the shim (i.e.: 280=2.80mm). They are available in 0.02mm increments.
The reason I am asking about the diameter is because the dealer tells me that they no longer carry the valve shims. There are other companys who sell the shims but they have a range of diameter sizes. I think they are 31mm but want to check before I order online.
Sounds like your dealer is too lazy to look them up and order them or doesn't know how to. Refer to part code "13201H" on the parts diagram link below. You will see the list of shim sizes in the list below the diagram under that same part code. When you find the size, you will see a part # with a "**" in place of the first two digits of the part number. Replace those "**" with the number "13" and you will have the part #.
I did give him the part number that's when he told me they are not available. This is the same dealer who told me the instrument cluster was no longer made but I was able to order it on line. The machine shop has boxes of shims but they do not look healthy and they do not have the oil hole. I need seven on the intake side and could use a couple on the exhaust side. That site is where I get some parts I will call to see if they still stock them. I did find that a number of other cars like BMW and Toyota use the same size shim but are more money.
For online Nissan sites, I use 1stAAANissanParts.com. Most of the online Nissan part sites are Nissan dealers, so if they can get the parts for you, your local Nissan dealer should be able to, as well. If you have another Nissan dealer near you, try calling their parts department with the part #s you need and see if they can order them for you. Why do you need so many shims, anyway? Did you install a performance camshaft or something?