Any advice for acquiring letters of recommendation for my army aviation packet?

What you can do is approach the nearest Army Aviation unit and develop a rapport with the Aviators. Don't just cold call asking for a recommendation from them without getting to know each other

Apologies as I have been sidelined for quite some time by serious health issues. Hopefully you received some advice. If not, my recommendation is to request FaceTime/office time with some warrants you are familiar with or acquainted (or feel comfortable approaching). Sit down, lay out your goals and understanding of how to achieve your goals and then ask them to critique your plan(s). Once done, ask them what it would take to get a letter of recommendation from them. Then follow thru on whatever requirements that they lay out. Apologies for the extreme delay. On the bright side I am almost able to walk again and might live to see another Christmas! Hooah!

Unless Warrants have changed since I retired... Just ASK, were really a laid back group of folks! Of course the best ones to ask are those you've worked for or with favorably in some form or fashion.