Lee Machine Shop.  Address in this forum.

I made a simple cutter from scraps of mild steel.  For cutting just a few shims there is no need to harden the steel.  You do need a lathe to make these cutters, and some means of squeezing them together.  I use a hydraulic press for that, but a decent vice will do the job as well.  The tool is made in 3 parts, the first is turned with a raised section that is the required size of the shim.  In the centre of this a hole is drilled to match the spigot on the second part.  The spigot on the second part should be a sliding fit in the hole and the diameter above that should be a neat fit into the depressed section of part 1.  To use this you need to cut a hole in your shim material (aluminium or brass) large enough to accept the spigot on part 2 (It doesn’t have to be too neat as this bit will be discarded).  With the shim material placed over part 1 and the spigot of part 2 through the hole in the shim, pressing down on part 2 will cut out the centre disc of the shim.  Then part 3 comes into use.  This has a central hole that is a sliding fit on part 2 and a relieved section that is the same diameter as the OD of the finished shim.  It is slid over part 2 and pressed down until it shears the shim material and passes down over the outside of part1.  After separating the 3 pieces, the finished shim washer can be put to one side and the scrap centre bit
discarded.

I used to do that with E-acto blades and scissors.  "Lee Machine Shop" only way to go.  A little expensive, but, worth every penny.  DOC Holliday