How does someone get a letter of recommendation from a warrant officer when they don’t have a warrant officer in their unit?

Your best bet is to introduce yourself at your closest AASF (ARNG Aviation Support Facility). I am sure if you walked into flight ops (or where your Flight Facility receives visitors), you will have an opportunity to introduce yourself and ask to speak to one of the Facility IPs. Most are open to giving a tour, answering questions, and if asked, may be willing to provide an LOR in return for an interview. Make sure you have a good chunk of your packet complete and with you. If a young soldier wanted an LOR from me and they had their documentation with them to make the sales pitch, I’d be inclined to hear them out. Additionally, the tenacity it takes to walk into a den of Warrant Officers to introduce yourself shows “people skills” and determination. All good things we look for in future Aviators!

Best of Luck!

I was just talking to the warrant recruiter in Sacramento about this yesterday morning (how do you get a letter if you don't know any warrants?)
I assume you are working with the warrant recruiter for So Cal.
The usual route is for the recruiter to forward the relevant parts of your packet (ERB, etc) to a few warrants at the aviation unit near you, (JFTB in your case), head over there to meet a few of them, and then have a more formal sit down interview with the CW3 who will write your letter.

Since you are in the guard, I assume that you are consulting with an assessions NCO. Often they have such contracts. Ask that NCO