Bob, Geoffrey is one of my recommended makers for low flutes. Make that a top notch one for low drones. That is an area where fewer makers shine, but Geoffrey makes great flutes in the lower range.
You might consider a D# (Eb), a D or a low C. I kinda think as a guitarist, you just might like the D# (Eb) a lot. When you get below low C, you are in the true low range, and below low A, you enter the contrabass range.
I just got a low C from Kuz that I really like a lot, myself, and I have a low C duet drone by Geoffrey, that is a fabulous flute. I also have a low C# drone from Russ Venable that really talks to me, and a low C from Russ Wolf that I love to play new age style on.
While I think Butch makes a fine low D, I have never found a low C of his that talked to me.
Below the mid range, I have a low B from Geoffrey, a low A from Leonard Lone Crow McGann, and a low B art drone from Geoffrey. Still haven't gotten the low Bb. I have a contrabass in low F#, and E, both from Pat Haran, who is the other really good low flute maker, I like. (Pat's are extremely easy to reach for their size.)
So......there are plenty of good sources.....you just need to decide what you are looking for, in key, and what price range fits with your need, and shop accordingly.
In D#, I have J.P. Gomez, Jack Thomas (art flute), and Butch Hall, at the moment. They are all good flutes, but they are all different, as well.
Still, you need to try to hear some flutes play, even if you ask the makers to play them over the phone. (Land line is best.) While you might not play the same way, it does at least give you an idea of tone.
I really do say, there are more good flute makers out there, than we can really know about, or can afford to buy from. Take your time in searching for the right flute, and try to make as good a choice as possible. You may need to live with that choice, at least for a time.
Everything I have learned about flutes, I learned because I had limited dollars, and lots of wants.

That meant I had to learn all I could, to seek out the best, at the best values. While some people wouldn't necessarily make the same choices, that's because flutes are somewhat individual, and we don't all look for the same thing in a flute. That is good, as it keeps flutes from getting to be just a "product". They still all have their own character, individuality, and unique suitability, to each individual player. So, even though we can offer some guidance, in who to look at, you must still decide for yourself, in the end, who has what speaks to you.