Hydrochloric Acid (HCl):
HCl can be produced on purpose (burner method) or as a by product. The burner method produces cleaner material with fewer impurities. 

Market Dynamics:
While there are many uses for HCl, the one market that can cause wild swings in Oil&Gas, since they use large volumes in drilling wells.
Most industrial HCl comes as a by product of Polyurethane (TDI), which is used to (primarily) to make car seats. 
Note: If Rig counts (Oil&Gas) go up and new auto sales go down, you could have a supply issue.

Up Stream Materials/Building Blocks:
Hydrogen
Chlorine Gas

TDI (By product)
​Titanium Dioxide (By product)

Down Stream Materials Consuming Hydrochloric Acid:

EDTA Acid
Keller's Reagent Aluminum Etch
Calcium Fluoride

Citric Acid

Fructose

Gelatin
Hydrogen Cyanide

Lysine
​PVC

Cleaning Chemicals

Leather Production

Steel Production