Morning Hans! There are a range of colours from various manufacturers that loosely cover your requirements; of course their use is dependent on what part of the model they are going to be used on. Some that I use are the Humbrol Metalcote series 27001 to 27004 (although some are described as aluminium they are inter-mixable to the precise shade you want - and are buffable to an appropriate lustre. Humbrol metallics 53 and 56,are useful,
Revell 99 is also very dark. Acrylics are a happy hunting ground for you; War Front (Scale 75) Black metal SC-63,
Model Air (Vallejo) 71.072 Gunmetal is good for washes. AK Interactive do a range of metallics and are excellent! I have all of these on my shelves and use them as and when required; although generally I create my own shades using a mix of a mid-spectrum metallic, a dark grey and a touch of blue, brown or green, A wide range of 'dark metallic greys' can be created. I mix in bulk initially using mini jam jars - the type you get from cafes, B&Bs, or hotels - then 'tweak' them as appropriate, I hope this is of use - happy hunting