1 of a kind DRAPER HILL cartoon (famous political cartoonist)

my mom in law was married to the brother of DRAPER HILL, famous political cartoonist who graduated from Harvard, also worked for the Harvard Lampoon, also worked at the Worchester Telegram (1964 to 1971) and ended his career at the Detroit News (1976 to 1999). The title of this cartoon is called RAILSIDE MANNER. I believe it is an original and looks like there is an 'overlay' of some sort on the picture where you see any ink /sketch marks. this is on approx 18 inch by 24 inch piece of thick paper/ almost poster board like (not as thick but close). there are some staining on the edge at bottom. This is believed to be created around 1966/1967. What do I have, what is the value and where do I find collectors of Draper Hill? any info much appreciated!
(no spammers please!!)