I've come across something called Bare Metal foil which I is self-adhesive. I've never used it (though I've had some aluminium sheets for years) but it comes in a shiny chrome finish. Here's a link to a UK supplier which I've used for other materials and is good.
http://www.hobby.uk.com/cgi-bin/hobbys-cgi/Catalogue.pl
It's been a while now since I have had the time to continue my restoration of my Silver knights parts.
After Gordon's post about Bare metal foil I looked into it and went ahead and bought a sheet from the US, because it was cheaper than anywhere else in the UK with Postage.
The finished look of the foil is the best so far for colour and depth of shine but it still isn't what I'm looking for. It also has it's limitations as to how it deals with curves and made creases that can't be removed. The instructions say that it may be necessary to use several pieces to cover awkward areas but this leaves joints.
Overall despite not giving the finish I wanted the product is easy to use and on flat surfaces does give a good mirrored look. It Isn't that hard wearing and in the toy box the surface can get damaged and any parts that lift can be peeled off very easily. So It is probably best used on display pieces and obviously ideal for making mirrors.
I have also tried another chrome spray that was said to be the best on the market but it is just as bad as all the others.
In the 2nd picture the parts are from left to right bare metal, original playmo silver and spray paint finishes.