Can cartoons be used for free by non profit groups or the education sector such as teachers?

In very selective circumstances I could consider this. For the most part, non profits do in fact have certain budgets, and any ancillary items such as graphics – which includes cartoons – should have a redeemable value when used in any kind of projects or campaigns.
As for any teaching related requests, it is advisable to email me with any details about how you want to use a drawing and give information along with your contact info so I can get back to you. When it comes to free cartoons in exchange for “exposure”, it is common knowledge that you can die from exposure!