I'm not sure what speedo restorers are available where you are but here in NZ the approach is to buy pretty much any chronometric and get it overhauled and at the same time converted to suit the a10 gearing, if you want the correct part numbers on the dial that can be done but most people in NZ don't seem to bother, and our local instrument guy prefers not to mess about making/printing one off dials anyway
Bezels can be changed to suit the type of mounting you have so that's not a problem to correct, the other major variation is side or bottom trip which might be hard for your local restorer to convert if you give him the wrong type.
One might have to wait a long time for the exact correct speedo to turn up, and even then how could one sure the internals match the part number on the dial!
I'm sure others will chime with some tips but that's a start!
Here's a link to one on sale but it will disappear soon...
http://www.trademe.co.nz/Browse/Listing.aspx?id=963973234