Manual or machine stamping? You can get brass type for manual stamping from bookbinding supplies, e.g. http://www.finecut.co.uk/bookbinding/

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=5575135717&ssPageName=ADME:B:SS:US:1

You could email stephensonandblake@btconnect.com which is some of the people from the late, lamented Stephenson Blake.

They aren't doing cast stock alphabets, but they do very good CNC machining, we use them for high frequency welding electrodes.

Address your enquiry to Neville Buckle.