You need just look cancer cell line databases with "correct" key words.
For example, DSMZ Catalog of Human and animal cell lines (http://www.dsmz.de) has at least two (but may be more) breast cancer cell lines derived from rats: ACC-485 and its derivative ACC-358. By unknown reason both of them are not appeared if one put the word "breast", "breast cancer" or even "breast cancer cell line" in the Search term. It needs to search these lines with using word "mammary" or "mammary tumor". It looks a little bit strange but may be helpful.
We use Walker-256 mammacarcinoma cellline combined with Wistar rats. It is working very well. Tumorgrowth in hindpaws is visible after more or less 3 days and growth than very fast, more or less in 4-5 days up to 1,5 - 2 ml volume.