Firstly, are you supplying materials for it, or do you want the machine shop to supply materials. If they are supplying it, then they'll need a chance to make sure they can get the materials.

What area are you in geographically?

You need to find out a price: with one-off works, much of the time is on set-ups. That said, I wouldn't have emailed the companies, I'd simply have gone round to the front door with a drawing and asked if / when it's possible. Many machine shops will be quiet at the moment.

Have a look through Yellow Pages under "Engineering Machine Shops", or "Precision Engineers".

PS, with your dimensions, express them as mm rather than cm (ie, 130 x 230 x 20, rather than 13 x 23 x 2) - and remember to state your tolerance (ie, maximum allowable deviation from the finished dimensions), that way the machine shop know what they're taking on.

Hope that helps.