Are there specific mass breakdowns for aircraft?
I can point you at some reference materials you can use. These methods involve estimates for different types of aircraft and formulas you can use to estimate the component weight based on the MTOW and OEW, for example.

You can use the following books:


Roskam - Airplane design (a series of books)
Egbert Torenbeek - Synthesis of Subsonic Airplane Design
Jane's All the World's Aircraft (over 600 aircraft)


scholar.google.com is another good source for finding articles about landing gear systems and design in general.