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.