Below you find useful online resources and journals for the study of politeness.
Linguistic Politeness Research Group: http://research.shu.ac.uk/politeness/
Journal of Politeness Research: http://www.degruyter.com/view/j/jplr
Journal of Historical Socio-linguistics: http://www.degruyter.com/view/j/jhsl
Journal of Historical Linguistics and Sociohistorical Linguistics: http://www.let.leidenuniv.nl/hsl_shl/index.html
Series: Advances in Historical Linguistics: https://benjamins.com/#catalog/books/ahs/main