Should I include a selection as an alternate in national competition awards on CV?
The two basic criteria I recommend using for answering questions on whether to include something optional on a C.V. are:


Are you proud of it? [note]
Will it detract from other things on the C.V. by feeling like "filler"?


I don't know the particular awards you're talking about or how competitive they are, so I can't make a specific recommendation regarding them.  At one extreme, being runner up for an award where only three people are nominated isn't very interesting; at the other consider how big a deal it is for a movie to be nominated for an Oscar even if it doesn't win.  See if you can find out how big the applicant pools were and how many alternates were accepted, and if it was highly competitive, then include it on your C.V. and also include the competition numbers.
I would also advise to err on the side of inclusion (people who don't care will just ignore it) unless it will detract by comparison from other things that you have won.

[note] Certain things are non-optional, of course, for the sake of honesty, even if you aren't proud of them: you've got to include things like internships, and all of your papers, whatever you might have done while young and naive.