The 42nd does not have an individual monument at Gettsyburg. It fought as part of J.M. Jones brigade, Edward Johnson's division, and took part on the assault on Culp's Hill on the late afternoon of 2 July. There is a tablet marking the general location of where the brigade was located, with a description of the fight for Culps Hill. I am sure one of the Park rangers can steer you in the right direction when you get there.