Thanks Cullz.
I found a local place that has lots of scrap MDF but nowhere I've seen plywood yet.
I'm a bit iffy on grabbing stuff from construction sites nowdays as in the past few years they have brought in HUGE fines if you pinch stuff, and Murphy's law says the time I grab some ply is the time they weren't intending on throwing it out!
Will keep an eye out though, there's a lot of new houses and units going up around my area.
ML
Contact some timber floor layers - they often use plywood as underlay - also shipping companies who often pack odd sized equipment in plywood containers