I am one of the guy using macro_cosmos test wafers, it is working out very nicely. More recently, I found a USA source for silicon wafers (https://www.ebay.com/itm/10-Assorted-Vi ... Sw4DVeALQn). The vendor is a collector of wafers! his ebay store lists several variety of these (price $25 and beyond). I got 4-inch assorted disk set for $40; each disk has numerous chips / resolution chart etc.
Enjoy.....
Silicon Wafers for Object Lens Testing
Moderators: rjlittlefield, ChrisR, Chris S., Pau