The NRCC has drawn up a map of all 435 Congressional Districts, separated them out by state, and linked each district to the website of either the incumbent Republican that represents it, or the Republican that will be challenging the incumbent Democrat in November.
Note that in cases of contested primaries without an incumbent (like, say, FL-05’s) the NRCC is explicitly not taking sides by picking any particular campaign to highlight; they’ll put up the website of a candidate who is the only one in a primary, which makes sense.
I’ve been playing with this feature for a bit, and the NRCC came through on this one: it’s straightforward, easy to use, and it’s going to save me a good deal of work. I suggest that folks use it, particularly if they feel the need to concretely express their disapproval of the latest Democratic Member of Congress’s shenanigans. And with 430 of 435 races being contested, folks usually can.