I'm a longtime metal clay artist and have made texture plates in a variety of ways:
1. at rubberstamps.net you can upload your art file. Good quality and choose just about any size.
2. use polymer clay. can carve a sheet before or after baking it.
3. photopolymer plates have been mentioned too. I use boxcarpress to get my plates. I also have a CraftCast titled "Enamel Illusions by Cindy Silas" that details making photopolymer plates, along with using resin and alcohol inks to simulate transparent vitreous enamel on silver metal clay.
4. I have a 3d printer and have used it to make texture sheets, but this isn't the best use for a 3d printer as a texture sheet is usually fairly flat.
5. with the Silhouette die cutter, you can cut a stencil from your design file.
and my favorite new method
is to laser my own rubber stamps! I purchased a 4W laser called the Emblaser 1 for a very reasonable price and put together the kit. This can be found at www.darklylabs.com
:)) Cindy Silas