I have a couple of sets of armor my kids have grown out of (or so they claim - I think they just wanted new pads). Make me an offer!
I'm super lazy, so I'll just repost some links.
Elbows/Knees
http://www.pinkbike.com/buysell/1968352/
Knees only.
http://www.pinkbike.com/buysell/1968398/
They're on craigslist too.
https://vancouver.craigslist.ca/van/spo/5612818109.html
https://vancouver.craigslist.ca/van/spo/5612824445.html