How to find old classic autographs and memorabilia?

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How do you go about finding such things? When I search on the internet for people like Ingrid Bergman, Bogart, Cary Grant, Elizabeth Taylor, or memorabilia from old movies I basically just come up with sites selling posters and such. We watch movies from the 40's and early 50's probably 90% of the time, so that's what we're really interested in collecting. Unfortunately almost all of the stars from that golden era have passed.

Is there a reputable place that deals in Hollywood items from that era? I'd be most appreciative of any help.