[Franciscomv]

I can't help you with the year of manufacture, but the model number should be on the frame, right beneath the the crane.

Open the cylinder and you'll be able to spot it.

 

[Franciscomv]

You're right, I forgot that the older Smiths didn't have the model number there. It does look like an M&P, but I'm not an expert (as my previous post proved!).

Here's a site with some Hand Ejectors and M&P's for sale:
Pre-war Smith & Wesson Hand Ejector revolvers