Louis Danziger 1966 LACMA Poster -

I have figured out this may be valuable - the problem is, I cannot find anything online except for Pintrest listings. I do want to sell it, but do not know the best avenue or even who to ask to get an idea of its worth.
Can anyone give me some suggestions.
This is a 24" x 18" original poster from the Los Angeles Museum County of Art, Lytton Gallery for an exhibit of American Paintings from the Metropolitan Museum of Art. Says Design by: Louis Danziger on the side. The date of the exhibit was June 1st-July 31, 1966. The paper is thick poster paper and is yellowed on the back The edges have slight damage, dog eared mostly- but not bad.