The Federal Election Commission has two, interactive maps connected to data that should be very useful in tracking independent expenditures on
Senate and House races. Senate or House races and the current and two most recent cycles can be selected.
Selecting the State for Senate or State and then House District gives a table which can be sorted in various ways and an advanced search function, as well.
The table gives information on the PAC, candidate supported or opposed, the amount and date of the expenditure, and purpose. You can learn whether it is for television, direct mail, or other.