The only gem to dxf conversion that makes sense, is export of vector graphics / shapes between GEM format and DXF format, typically to recover ancient vector files and save them in format useable in modern software. Not many graphics software still support GEM format, you will probably have best luck with CorelDRAW. But you can still find old GEM Draw on some abandonware websites, so perhaps this is also viable option, but you need computer for MS-DOS or virtual machine for that.
Updated: August 29, 2023