Hello,
Dont waste your time, you will never find someone who can bring you the .cpp, .h files from a .so library. This is IMPOSIBLE, a binary file can NOT be decompiled to a source file. You only will get the assembler source code, so if you are good (or your employee) it can be taken, readed and modified.
Note: .so file is a library file, this file is a binary and binary is not like a bytecode (like java or actionscript).
Best regards,
Edixon Vargas