In a former life as an AP for a relatively small-time PBS series, I was often tasked with submitting similar requests to various networks, etc. The standard operating procedure is to spend months on phonecalls and letters to every company involved with the production, then on the outside chance you successfully finagled permission from all of them, send in every dime you have ever earned in your life … along with a contract stating that you will send in every dime you ever earn in the future. In other words, even if the History Channel would sell you their footage or animations (personally, I trust Shane’s advice that is a dead end), don’t expect it to cost anywhere near the relatively nominal costs of buying “stock” footage/animations or even having your own footage shot and animations built. You have to understand that having their content show up in your production detracts from the value of their production so it takes boat loads of cash to make that worthwhile for entities that just aren’t in the business of selling their source footage or animations.