Sorry I worded my response in an unclear way. I do not experience this issue with the CHARMM36 force field in Gromacs.
The link I downloaded the force field files from (http://zarbi.chem.yale.edu/oplsaam.html) shows “CHARMM and Gromacs formatted parameter files for the OPLS-AA/M force field for proteins”. The first two links show file formats for the CHARMM package. My second question was asking if I could assume that since the atom types I need are missing in the Gromacs files would they would also be missing in the CHARMM formatted files.