http://www.ebay.com/sch/i.html?_from=R40&_trksid=p2050601.m570.l1313.TR0.TRC0.H0.Xdragon+ball+z+laserdisc.TRS0&_nkw=dragon+ball+z+laserdisc&_sacat=0
They usually hover around $50 a movie but some are cheaper.
I bet Yahoo Auctions would prove helpful as well.