Okay, it's sacrilege on this form, but ISTM it should be possible (even pretty easy) to process a digital false color IR image to the same color response as the Kodak film product (assuming you can't find a color IR that does the job). Whether it's financially feasible with your budget having to run through Congress is another question.

The other (locally acceptable) option might be to shoot B&W IR (Kodak has also killed their 70 mm IR, I believe, but it should be a little easier to replace than the color IR) with synchronized frames in two cameras with different filters, and examining the images with color filtration that picks out the infested trees. Come to think of it, though, with Maco killing off IR820c and the 400 version not yet available in larger formats, I'm not sure there's a deep-IR emulsion available anywhere in 70 mm (you need perfed, right?).

Might check if there's a motion picture emulsion that will work for you -- buying a couple thousand feet doesn't sound like it'd be a bad thing, if you have the budget, but you might have to invest in processing machinery too, since a lot of motion picture stocks aren't straight C-41 and very few if any in that size are E-6. IMAX gets their 70 mm film from somewhere, though...