Gromacs topology files for common RTIL ions are available at https://github.com/olunet/RTIL-FF. Most of them were written in 2012–2013 by Isabel Lage-Estebanez and Vladislav Ivaništšev, and tested in MD simulations of ionic liquid bulk. Some, like FEP-anion and B(CN)4-anion, were added recently and are not well tested. You are welcome to try and give the feedback at GitHub.