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