Unfortunately for a vintage sm300 there is no rep option from the so common sources; case shape and dimensions, dial size, bezel shape and assembly, insert, etc... are all far away from the real mccoy.
The only decent option is a vietnam rep, the most accurate I know.
i found one in 2018 and share some pics of it (case has correct dimensions and made to fit a cal. 550 omega mvmt, 27.5mm dial, 60 click bidirectional bezel and a mil engraved caseback).
It has gone through relume and dial ageing after a minor accident and is now waiting for a custom made plexi insert.