This from a very tall Viking friend of mine! He lives in Yorkshire, but I don't hold it against him ;o))
"I know there are people out there with an interest in model engineering so I thought I'd pass this site on.
I've used this company for many years, it's where I get my Copper and Steel Mushroom head rivets from at a very good price and much cheaper then most traders.
They also do matching rivet bits/dollies and supply various sheet metals which they will cut to size if you send them a template. If you don't see what you want give them a contact. The url is
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"Regards,
Kim Siddorn