I lost the actual eyecup a long time ago, but I finally got around to making another. I didn't have an actual Olympus eyecup to model this on; I did this by looking at other peoples designs and pictures off the web. I printed it in two halves and superglued them together, and it fit quite snugly, but if you want to try, I also uploaded a complete model of the eyecup.
This was designed for an Olympus OM-D E-M10 Mk1. I don't see why it shouldn't be compatible with other OM-D cameras, but one commentor said it specifically does not fit the E-M10 Mk2. I don't know about any other models. The sketchup file is available for editing.
Printed in PETG. I recommend printing it in two halves and gluing them together, but you can try printing it in one piece.