This organization collects all sorts of election results and information about upcoming elections including special elections. There's a learning ramp on how to make good use of it, so below is an example of how you can determine what special Senate elections this year are merit our attention. The results were: protect Kelly AZ, Warnock GA, Masto NV, Hassan NH. Try to flip Blunt (Missouri), Johnson WI. This was on a search of a 4% or less margin of victory in previous election. Obviously, all this will change as time marches on and opponents throw their hats in the ring. At that point we have to switch to polls again. Furthermore, margins of candidates seeking re-election after six years are pretty old data.
League of Women Voters
The League is dedicated to ensuring that all eligible voters - particularly those from traditionally underrepresented or underserved communities, including first-time voters, non-college youth, new citizens, minorities, the elderly and low-income Americans - have the opportunity and the information to exercise their right to vote.
Locally, we love the Concord LWV for the non-partisan debates they hold for candidates, education in schools training students to hold voter registration drives to sign up their peers, and their detailed, well thought-out position papers on legislation, and educational events.