The significant dimension is the thickness. The acid etches sideways (underneath the etch-resist), as well as down. If you're looking at the type of sheet thicknesses used in model making (10-20 thou, give or take), you could try PPD in scotland. They have done etching for me & will make up the tooling if you don't have suitable computer software.
Try them on
enquiries@ppdltd.com or 01546 602963.
Hope that helps. There are others, but some are cowboys & others will only etch, not produce tooling or artwork.