I had a similar problem about 3 years ago: all the "exhaust" paints seemed to have disappeared off the market. I did find black, but I like silver downpipes, and prefer silver silencers, too.
I then found (on eBay) a tin of silver exhaust paint (up to 450C, it says), which has worked well. Put on a clean surface, it doesn't flake off, though does thin over time. Re-coating in situ is easy, though, as it's water-thin and non-sticky, if you're quick.
I've just dug out the tin, and notice that it's labelled in a fairly low-budget way (so perhaps the seller was selling on in small quantities, from a bought in larger supply?). Anyway ... all it says by way of supplier's identification is:
SMC systems T: 07407 710 157 E: smcsytems@hotmail.co.uk
(Note that I have spelled the email address exactly as shown. I suspect, though, that it should have an 's' in the middle!)