I remember Woolworth's used to sell hammer finish paint. I know they've gone under, but maybe Wilko's or similar may be able to help?
I think it was made for Woolies by McPherson Paints, but my memory may be playing tricks on me.
Wickes also do hammer finish paint in 750ml cans, but it's not cheap.
http://www.wickes.co.uk/paint/metal-...at/metalpaint/