ikea market it as wooden venetian blinds, but boot fairs are also a good source, I can usually pick up 40 48" slats in a blind for a couple of quid, a fiver if they are really holding out, from each slat I cut a strip from each side avoiding the cutouts for the strings about 3/8" wide to 1/2" 80 planks for a few quid. if you get 3 blinds for a tenner that will keep you in planking for a good few models.