I need to buy some metal to do some chassis repairs on my car, so need some thicker stuff (2.5-3mm?) but I only want a small amount, 2x A4 paper size...

Where could I buy some off cuts?
I've asked 3 metal yards, my mates body shop and a mechanic mate with No joy.

What sort of place do I need to go to buy some?
Or would b&q or euro parts or someone like that sell any?

Or anyone on here in South London that's got any?