Hi Sheila, I don't know if you're truly looking for dropshippers (are you?

) but just to go with your example - there are tons of forums and groups for just about any niche you can imagine. Google turns up quite a few good leads for a search for '
dropshippers forum'.
No doubt there are also industry events, newsletters, and possibly even print magazines for dropshippers...
Continuing with the same example: you can also search Twitter, LinkedIn, and Facebook for the term 'dropshipper' and follow/join conversations, groups, etc. and follow the links they're sharing to even more sites you can potentially interact with your target market.
Also, look for dropshipper blogs, read the comments, or comment yourself, and follow links to see where people are coming from/going to.
Of course, this approach would be effective for any niche or industry... Hope the suggestions help you find what you're looking for