The Op shop on Glenhuntly rd, I think it is 1134 Glenhuntly rd is advertising a clearance sale. Not open Sunday and I think only half a day on Saturday.
While you are in the area worth checking out the Retro Homewares shop on the same side of the road but further away from the city, between the railway line and Grange Rd, fantastic 70's gear. Its not an Op Shop but worth just looking, great stuff, Orange and Lime green predominates.
Further down on the corner of Glenhuntly rd and Grange Rd is the Posh Op Shop. The prices on some items are higher than retail, hard to find a bargin but worth a try.