To be honest the best way of getting your mini hat back into shape is to use a little water and then stuff it with something to get it back to it's original shape.
Damp the sinamay down and then either pop is over something like an uptunred glass or candle (something that will push the dent back out) and leave to dry.
I make mini top hats and fascinators and travel around to shows and events with them, so they get bumped around a lot in my bags. Generally they are okay, but once in a while you get a dent.
Sinamay is already treated, so you shouldn't need to add anything else to it - but if you do, use sparingly as stiffeners leave marks on sinamay that is hard to get off/out. Also as it is a wide weave it tends to soak straight through.
As to millinery supplies try these
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