First, you could always find the antiques roadshow :-)
Second, there are associations and you can contact them for recommendations.
Third, never - never tell the appraiser you are considering selling. Next thing you know you have lower prices and they, or a shill, are making you a ‘fair market’ offer. If you have no clue as to price, contact an insurance firm and request a valuation for insurance purposes only. You wish to keep the goods and insure them for a fair value in case of damage or theft or fire, etc. You’ll at least know, then, the ballpark of value so you do not get ripped off.
You can also go to a trade show. Like for baseball stuff or whatever. Look around. You’ll probably find identical items. When it comes to some things, though, just because it looks that same does not make it so. Therefore, a lot of homework is needed.
Just for the record, I have never (and would never) do this. It is unethical.