Maciej Ceglowski of Pinboard has been traveling the country meeting candidates for races that professionals helped identify as underserved by the DNC, and came up with a "Great Slate", which is a good starting point:

https://secure.actblue.com/donate/great_slate

But: if you live in a major metro area: you're probably in a D district, where just a few miles from you there's a suburb in an R district. Find that district and see who's running in it.

Here's who's running in the NM-2:

http://fec.gov/data/elections/house/NM/02/2018/

Just fix the URL for whatever race you're interested in.

Strong recommend on donating to the Great Slate.