You can leave them blank. Judges hardly ever get voted out. Google is a good idea, or search your local newspapers' archives. If you know any cops (sgts or better in vice or narcotics, likely to have lots of court time) or court reporters they will have the poop on the judges. Ask more than one and be prepared for some hair raising stories. Lots of judges are completely whacked.
As for the DA, you're just SOL. If you don't want to run up the DemocRATs vote count, just leave it blank.
If you haven't already, get a sample ballot (available at county offices and libraries usually) to study and mark-up before you go to the polls. You can take it with you to vote. That way you don't forget any important issues, or accidentally vote in a way you didn't really intend. The ballot this year is huge so you will really want to mark-up a sample ballot prior to voting.
If you did not get the "Blue Book" (explanation of ballot initiatives by the state legislature) you can go to
CO Secretary of State's Blue Book web page. Also your county should have sent you a "TABOR" notice. This is usually a small newspaper looking pub that explains all of your county level ballot initiatives. You'll need it to fully mark-up your sample ballot.
Good luck and thanks for voting.
Vote NO! on 36!!! Don't dilute COs' electoral votes.