Not quite canvas covered, but almost...Nearest available specimen....
There's a very tatty looking once-painted Perrybuoy hanging in Andy Seedhouse's emporium for which he would like £20.
You will find a couple more hanging in Eversons' shed - not actually Perrybuoys I think.
If you walk in the other direction to Robertsons, Rollo on the "Brightlingsea" has a huge stack of decent ones but he needs them for the MCA...he may know where to get more.