...Unless you stashed a vial of sulphuric acid from a school science lab you'd have a bloody hard time getting your hands on sulphuric acid. And if you're going down that route why not bottle some ammonia too and sniff that for kicks
As mentioned, Marquis contains both formaldehyde and sulphuric acid. Sulphuric acid alone is often used in forensics as a reference. MDMA will produce a purple--> black with Marquis and a purple/red with sulphuric acid. MDA will produce a purple with sulphuric alone.
HCl cannot be used as a replacement for sulphuric acid in Marquis.
I would presume any OTC product containing formaldehyde in solution would also contain a small amount of methanol, as it extends the shelf life considerably (slows down polymerisation which makes a formalin solution white, and Marquis brown)