Here is the quickest way to get one. Order two, they are not going to carry them any longer.
http://www.midwayusa.com/product/291088/ruger-pawl-spring-blackhawk-super-blackhawk-bisley-vaquero-bisley-vaquero-single-six-single-six-bisley-duplicate-of-116-904
If yours is lost the plunger is lost also.
http://www.midwayusa.com/product/456204/ruger-pawl-spring-plunger-ruger-blackhawk-super-blackhawk-bisley-vaquero-bisley-vaquero-single-six-single-six-bisley-blue?cm_vc=OBv1291088
I have a couple spares but don`t want to give them up. I would just have to reorder to keep my spare parts up.