There's a COFF 2 OMF tool somewhere on digitalmars.com. Don't know how good it is though, and can't say anything about reverse conversion.
There is indeed a coff2omf tool for static libs and here's the funny thing: you have to pay for it :D Like it wasn't enough to torture people with dmc,optlink,cv,omf and other dinosaurs ^^ (but seriously, that toolchain has already made competent people turn their back on D: http://h3.gd/devlog/)
A free one is only available for import libraries, it's called coffimplib and pretty hard to find on the site.
