I can't recommend a dealer as all my vintage watches come from eBay or antiques fairs , what I can recommend is doing a massive amount of research before you buy .
My first vintage watch was a gold longines flagship purchased at auction , later I found out its a franken watch . Movement comes from a Stainless steel. I didn't do any research before purchase, lesson learnt!
Post up some some decent pics of watches your interested in with movement and caseback shots , there is a few of us on here that maybe able to help.