Formulary doesn't sell EDTA free acid either, only disodium and tetrasodium version, and neither of the two can be used directly for making Ammonium Ferric EDTA. You can make EDTA free acid from EDTA Disodium Salt by dissolving as much as possible in a liter of water, then adding a strong acid like Sulfuric Acid or Hydrochloric Acid. There is a chance that Amidosulfonic Acid or Sodium Bisulfate also work, but I would not expect Citric Acid or Acetic Acid to work. As long as the acid is strong enough, EDTA free acid will precipitate, because it's barely water soluble. Add acid ling enough to precipitate all the EDTA, then filter and wash the precipitate. After the precipitate is dry, which takes a few days, you can use it as EDTA free acid.
That's how I made my E6 bleach in the last couple of months - it works.
PS: If that's too much hassle, you can order Ammonium Ferric EDTA 50% concentrate from Fototechnik Suvatlar.
PPS: Ammonium Ferric EDTA based bleaches are extremely weak and take a long time. Most commercial Ammonium Ferric EDTA based bleaches contain a bleach accelerator, either 1-Thioglycerol or Mercaptotriazol. You can get the latter from Fototechnik Suvatlar, and of course from all the professional chem suppliers. Use it at 0.1 g/l, if you use more, it will slow down the bleach!