I recommend an antibody database available at labome.com. For antibodies to RET for IHC you can use the following link: https://www.labome.com/review/gene/human/RET-antibody.html. Epitomics has RET antibody (Epitomics, 3454-1) used in immunohistochemistry. Also, Abcam offers RET antibody (Abcam, ab1840) was used in immunohistochemistry - paraffin section on human samples (Ding et al, Exp Mol Pathol. 2013). In addition, R and D Systems provides RET antibody (R&D systems, MAB718) used in immunocytochemistry on human samples (Fattahi et al., Nature 2016). You can check the references and the description of these and other RET antibodies following the links.