There is a carboot in castlebar the last sun in the month 9-3pm I think.
It was good last summer as I bought a few things, but went to it last month and mainly traders, however I think people where waiting for the weather to get better, Im sure the private sellers will be out from now on. Am looking at doing one myself.
There is one on the Headford Road in Galway every sunday as far as Im aware. Havent been yet.
Cheers
c