You can search in Labome.com, where you can find an antibody database. In particular, for antibodies against c-Jun, you can check the following link: http://www.labome.com/review/gene/human/c-Jun-antibody.html.
Santa Cruz provides several rabbit polyclonal anti-rat antibodies against c-Jun: sc-44 and sc-101721 (reference: Yang et al., Cell Physiol Biochem 2015) and mouse monoclonal sc-166540 (reference: Wei et al., Brain Res 2014), suitable for Western Blot on rat samples. In addition, Santa Cruz has a rabbit polyclonal antibody SC-1694, which was used in chromatin immunoprecipitation on rat samples (reference: Hung et al., J Biol Chem 2015).
Also, Cell Signaling Technology provides a rabbit monoclonal anti-c-Jun antibodies 3270 and 54B3, used in western blot on rat samples.