I wouldn't know about any plug-ins. I'm looking at vers 4.4 (which is somewhat old) and it will convert both to and from EPSF and PS file types. And looking at vers 4.8, the latest, these (and many more) are supported. I do see that importing epsf files requires software that will open those files, but exporting does not show a limitation about plug-ins. Perhaps all you need is to download an update.