It doesn't have to be a real helmet.
Anything helmet-like will do the trick.
It should be of solid structure...
Made of metal...
And it should fit around your head.
A metal pot will suffice.
Where could you find a pot?
Pots are cooking utensils.
And they're usually found in kitchens.
There's a pot underneath the rear table in the SCUMM Bar's kitchen.
How do I get into the kitchen?
Take it to get yourself a helmet.