Beth,

You want 100 proof alcohol for tincturing; likely your safest bet would be to buy organic grape alcohol (190 proof) and add distilled water to make it 100 proof (you'll have to 'do the math' on the ratio of 'water to alcohol', I only 'do math' for me, lol).  It is VERY expensive ($150 per gallon, plus shipping...and I think that 190 proof alcohol is considered 'hazardous' as far as shipping, so there's likely a big 'haz-mat' charge on top of the regular shipping cost) http://www.organicalcohol.com/index.php?src=gendocs&ref=HowToOrder&ca...

While I realize that you don't want to 'risk' using regular vodka or other alcohol distilled from grain, I want to get the following information 'into print' for other readers...

My past research (and what I've just now 'quick googled' to paste below) solidly shows that the distillation process removes gluten, and that there are celiacs worldwide that are fine with vodka (and other distilled spirits), even if they were distilled from wheat or other grains containing gluten.  

From celiac.com:

Q: Even though most vodkas are in fact distilled from grain rather than the much thought potato, are they still all gluten-free?

A: (Scott Adams): Yes, distillation removes all prolamines so distilled spirits are considered safe.

***

I'm not quite sure what the point is of this particular list. Of course no one should consume anything that makes them feel badly. However, all speakers at a recent Celiac conference at Stanford University, including chemists, researchers, doctors (including Gail Pyle, herself a Celiac), and dietitians, were unanimous in their agreement that distilled alcohol, like vinegar, does NOT contain gluten unless the gluten is added POST processing.

The problem with the handful of reactions that are reported from distilled grain spirits is likely "contamination" (or incorrect distillation) - we can see on celiac.com that some people report having reactions from various distilled grain alcohols...but that most were in bars or restaurants (no bar or restaurant is 'gluten safe', due to cross contamination). 

I have also found reports of various alcohols made from gluten-free produce/grains having caused reactions in celiacs...which (again) is likely due to contamination of whatever may be added (or accidentally added) in the distillation or bottling process.  Many distilled spirits have 'flavoring' added AFTER distillation.

I see many reports of celiacs saying Smirnoff vodka is non-reactive, and Smirnoff makes a 100 proof vodka (I'd say it's 'safety' is likely due to 'triple distillation').

Blessings,

Unyquity