'Dear me!' is just a variant of 'Dear,dear!', 'Dear Lord!', 'Oh, dear!' and so forth. The earliest recorded use of it is in 'SheStoops To Conquer', the play by Oliver Goldsmith first performed in the 1770s. 'Says you' - often presented in the form 'sez you' - is just a jocular, uneducated version of 'you say' which has been in use since the middle of the 19th century.