Sorry, my edit didn't work. I did spot it in Gen III and tried to edit, but my phone doesn't approve....The selection Process in 5th gen and 6th Gen, it almost totally picked at random. Some Pokémon Starters, ledgendaries and a selection of special Pokémon are not on the random list. Furret was actually picked up during 3rd gen: http://serebii.net/potw/162.shtml (While it's not linked anyware on the site, you just need to know where to look or use the search option.
According to Smogon.. Furret is NeverUsed regular and I don't see it changing.. Personally I think it could be time consuming when using "competitive" Pokémon to complete against most NPCS.
And, well, I don't look at Smogon. It winds me up, but that's something else.