How to go about obtaining large amounts of obscure data?
I do not think that there is a general strategy to obtain obscure data other than:


Think about who might have such data (legally and ethically).
See whether they provide this data for free.
Ask them.


You may have luck in crowdsourcing steps 1 and 2 of this process on Open Data Stackexchange, half of whose questions are data requests. However, given the nature of your specific enquiry, I doubt that you will be successful there, as such data is very unlikely to be open.