Try 'bakara' or just 'baka'... Plurals are hardly ever used in Japan.
The only one I can think of is 'yatsura' from 'yatsu'

  If I'm wrong, I deserve to be flamed to a crisp. I'm teaching myself
japanese. The plural for baka would be baka, endings adding ra to nouns are to
make an adjective, so 

  Ranma no baka  --  Ranma is an idiot

Yeah...

  Minna no baka  --  Everyone are idiots

Hai...

  bakara         --  Idiotic

I thought that adding 'na' did that... But 'ra' is definately the
plural... 'yatsu' = 'jerk/fellow/etc', 'yatsura' = 'jerks/fellows/etc'

  PLEASE! correct me if this is wrong. One of the dangers of self study is you
keep making the same mistake until you embarrass yourself publically.

Kun-chan...