Wanted: M42 screw mount Pentax / Praktica lenses

I'm looking for some inexpensive M42 screw mount lenses. From a Charity, I have purchased a box full of old Praktica, Zenit, etc, cameras try to repair / revive and get working. None have lenses. I'd like to get at least some of these SLR's back in use and into the hands of people that could appreciate these 'classics'.