Contact the National Rifle Association, and ask for a referral to a member dealer in that area.
you can get it from an appraiser or at some antique roadshows.
go to http://gunbroker.com/
Library, internet, Standard Catalog of Firearms.
Go to an appraiser.
Perhaps a good place to start would be to find a copy of Flayderman's Guide to Antique American Firearms- you may be able to request a copy through your local library. This is a fairly comprehensive book with good descriptions and illustrations of thousands of antique firearms. You might also check for gun dealers in your area that know antique firearms, or check out a local gun show, where dealers in antique firearms have been neatly gathered in one spot for your convenience.
In firearms, antiques are LEGALLY defined as made prior to 1899, OR muzzleloading firearms. Newer than 1899, they are old, but not antiques. My best reference is Flayderman's Guide to Antique Firearms. You may also find a dealer or collector that can share some information with you. Check for gun shows in your area.
A great place to find an appraiser for vintage motorcycle helmets is to check with a local antique shop. If they couldn't help you, they might just be able to recommend someone for you.
To find the age and value of an old tapestry, consult an appraiser. An antique collectible may also be able to help you find this information.
This is tough, as only 50 of these jewelled Faberge eggs were made, and only 42 of them survived. There is an option to have it valued online by a specialist, but this will take up to 24 hours to complete.
Flayderman's Guide to Antique American Firearms
Your best bet is to find a reputable appraiser for any collectibles you think of value.
Hire an appraiser or have an auction house that deals in those item evaluate it for you. Either will charge you for the service.