Not sure what you mean by a few materials with the same BOM. A material can have multiple BOMs and can appear in multiple BOMs of other materials but different materials in the same plant pointing to the same internal BOM number I don't think this should happen. As far as I understand PP and I don't claim to be an expert If this did happen it would represent a serious internal inconsistency and so there isn't a standard transaction to find them. The transaction CS14 is just to compare two BOMs side by side and so won't meet your requirements. The table MAST connects material and their BOMS (i.e. the ones that build them not the ones they are components of) so you might be able to extract the information you are looking for from there but I don't think I can be of more help without understanding your requirement better.
I think this question might do better in the SAP ERP Manufacturing - Production Planning (SAP PP) space rather than the ABAP space. Maybe a moderator could move it or you might want to try re-posting it there.