Yes, you do have ethertalk for an Apple IIgs.
Grab a LocalTalk to EtherTalk adapter. Plug it into the printer port of your IIgs. I'm not sure that it will work with the latest version of Mac OS X, but I have definitely used it to connect to iMacs (ethernet only) and Linux (appletalk will not go over a rs-232 port, at least for macs).
Yes, I know this is cheating because you won't get ethernet speeds. But at least you can interface an Apple IIgs to newer hardware or non-Apple hardware.