I didn't have to.Simply installed and Google Play etc was all on there.
I installed the Gapps listed in this thread and it made the ROM act really weird. I then installed some from another source and they just seemed to overload the memory so I gave up. My phone was running with about 25MB of free RAM and I only had whatsapp, keyboard, system and something else running. Not good.
But someone did upload the gapps in this thread using the filename gapps-jb-20121017-KonstaKANG so a quick thread search should help you get what you want. Hope this helps.
I have flashed gapps-jb-20121017-KonstaKANG.zip, but when I am trying to open play store it instantly closed without any error message.