Watches

I'm looking to purchase a watch which belonged to my granddad. We no longer have it in the family.

It's a Seiko SGEG67P1 - nothing special on its own but has sentimental value to me as he wore it a lot before he passed away. I can't find through google.

Where are good places to look for specific models of watch? Where might one turn up? Are there any markets/ websites / forums one should know about?

Thanks :)