After finding and painting those mini canvases, I found some larger ones in Wilco.
And they had cheapo canvases also, so I bought some. They were 8″ x 8″ in size and in packs of four for less than a fiver. I bought lots and I have been smearing them with coloured mud (as James Elkins likes to call it )
Here’s one I did earlier (as they say). The more perspicacious of you will know where this is.