Not long ago, I was researching the scaling of converging-diverging de Laval nozzles to subminiature (1.5 mm throat diameter) dimensions for a non-rocket application, and later on studied the potential for making Cubesats fly around with thousands of m/s dV of hypergolic chemical rocketry. (A man can dream.)
Strangely, I found remarkably little information on either topic. Most high-dV cubesat engines are a variant on ion engines, and there seem to be no "subminiature" chemical rockets either in literature or in vendor portfolios.
There are plenty of full-size and "miniature" rockets meant for RCS jets, and there is a tremendous amount of research on "micro-scale" MEMS-based monopropellant rockets you need a microscope to see with fuel tanks smaller than a milliliter, but I couldn't find any information on a chemical rocket engine around 4 to 10 mm in diameter.
Is there a compelling reason for such a thing to not exist even in discussion? Or, alternatively, is there a clear counterexample?