The most well known reference source are The Scott Catalogues. The 1982 set I have has four volumes covering the world including the U.S. plus a separate specialized volume for the U.S.
Some libraries may have these on hand or you may be able to borrow them through a inter library loan. Try to get the U.S. specialized catalog. You don't need a new edition as this is an older stamp.
Likely not worthy anything and likely very common. The missing perforations on the lower left edge will greatly reduce any value as well as being slightly off centered.
Stamps can be reissued over the course of many years and there may be numerous minor color variations; different sized perforations, watermarks, being issued in coils as opposed to sheets, different papers, printing techniques, minor changes in the design and so forth.
