I've been watching all the blooper vídeos online and I can't seem to find an actual season 5 one. Even in the packaged "All friends Bloopers", they are only 1-4, 6-10. Did that season's DVD not have them in the extras?
I just talked to my friend who is crazy nuts about Friends! She said there is no gag reel in the season 5 DVD, but in the season 6 DVD she recognized a blooper that belongs in the 5th season. Hope that info is of help ☺
I think I remember them having clips at the end of the finale, during the credits in season five. I'm not entirely sure about some of the bloopers in season six, there probably is, but I'm mais aware of the bloopers during the credits of the finale in season five. :)