You can order them super cheap and in bulk from a variety of retailers. Ranging from simple toy things to rolls of it

Link me?

The feature size is pretty small for diffraction gratings. There are printer beds that will do the same to the bottom of your print as is done with this chocolate. None of the hobbyist models could get even close. The feature size is somewhere between 1 and 10 micrometers which is a couple of orders of magnitude finer detail than most 3d printers.

They are normally manufactured with other methods, but here’s a paper about printing them https://asmedigitalcollection.asme.org/IMECE/proceedings-abs...

So it’s possible, I’m sure they aren’t the only ones to try it.

no, not really -- BUT -- you can print onto the top of a grate to apply that surface finish to the bottom of the print.

It's a neat thing to do when you're printing phone cases or something similar.