Great Ideas! I am partial to the Dr. Horrible or Captain Hammer Idea myself
For Dr. H's gloves, I think a hardware store might carry them. Not sure about the welding goggles, but you might be able to find it there, too. I know the perfect place around me, but I think it's a one and only store. The place I have in mind is a hardware/gadget surplus store. It's where everything from gears, to baby spoons, to use LED cables can be found and it's amazing. Maybe there's a store like that in your area? As for the boots, I always get lucky at a thrift store like Goodwill.
I admire your skills to sew a lab coat for Dr. Horrible. Good luck!