Are achievements still attainable? 50th Post!

Can you still get achievements? @Kevin_MCX I have a few but there are some that sound like I should have also how do you get ones like Identity theft, know your canon, 117 communications (I have 179), Spartan, Master Chief, and others in the pictures?

P.S.
50 posts?!?! That's not much considering I've been here for 3 & 1/2 years.