There are all kinds of resources..most freelancer sites have people that can do this in a variety of formats, from whiteboard sketch videos to whiteboard/animation to full animation to mixed media to .....
Try Freelancer, Odesk, Peopleperhour, or Thumbtack.
Will say that many of the respondents will be offshore and some incredibly cheap...I have had good and bad experiences. Be as detailed as you can be in your posting, ask a ton of questions, get a timeline agreed to, and track the progress (or lack of).
Most of these sites have moneyback guarantees for the work performed, but if you decide to simply not proceed once you post your gig, some do take a 10% out of the money returned. Most require the total price you accept to be escrowed and then can be released on a milestone basis if the project is large.