Where to find boiler plate NDAs or Contractor Agreements?

I've seen https://opendocs.com/ recommended for this sort of thing.

Honestly, I know "googleit" is kind of a flippant answer, but that usually works better for me for this sort of thing than hunting around specific sites.

The bookstores use to carry books with various templates for these. I am sure you could probably find a book online to purchase.

There are also online companies that sell various sorts of things. I would not want something too generic as you may need to customize if for the local laws where you reside.