Long plank/tree section for shelves (Central Hackney, E8)

I'm looking for a rustic board, about 2m long and 20-30cm wide, 4cm or thicker, with the natural bark edge. Any hardwood is fine, and it can be rough, unfinished or a bit weathered. Perhaps left over from a felled tree or garden clearance? Happy to collect from anywhere within about 10 miles, ideally of east London. Thanks!