Would they provide HCl for us?
HCl was specifically prohibited in the rules, so unless that's changed, no. However, supervisors may provide written descriptions of a substance's reactivity with HCl.
Actually, that's not true. You're prohibited from bringing your own HCl, so you couldn't even pack it if you wanted to, but the event supervisors can choose to put bottles of HCl at certain stations. It's, of course, always dilute and you'd really only see it at stations with calcite or dolomite. They can also just write "this substance does/does not effervesce when HCl is added", like you said, but they can certainly provide HCl for some stations if they want to.