John,
There's several things you can use. Bare Metal Foil makes an Ultra Bright Chrome......it's a little harder to use that the normal aluminim colors, but it works very well for mirrors.
Another thing I use a lot of is mirror finish self adhesive Mylar......or even normal mirror Mylar would work too - all you'd have to do is glue it on.
I picked up a roll of this stuff somewhere many years ago.....and it's got enough on the roll to do about 7 million 1/35 or 1/24 mirrors. I'll never run out.
Bare Metal Foil can be obtained directly from their website:
http://www.bare-metal.com/
Good luck!