Probably best to speak with Sunny Hill directly and see if they have any representative in the UK, or prepared to send it across. Or try somebody like Pacific Tool and Guage.
www.pacifictoolandgauge.com
they have lots of details about export on their website.
Or if you are any good with CAD - draw up the parts abd send it away to steel CNC shop to run it out. Alternatively do it the old fashioned way and start with solid and rough it out and then machine/ grind / file to to shape.
Or totally forget bottom metal and make a blind internal magazine.