Toy hard hats can be found in costume shops or in places like toy's 'r' us, mr toys toyworld. Fake tools can also be found there, like bob the builder stuff that could be modified.
Not so sure about the giant wrench though, ebay? or cardboard and glue.
biggrin Overalls can be found at either work uniform shops (some have wesites) or your nearest clothing outlet. (Most are in the female section though I'm not sure for people in the US though.) Or check Ebay who knows. And the gloves can be found at any hardware store under the gardening section, same with the tool belt. The belt can also be easily made out of faux leather/material.
Spray paint some knee pads you can get at bike shops, sometimes you can find them in colours.
You can also get iron on patch paper that you can print your designs onto. Look in craft shops for this.
Goggles can be either made from scratch or bought via etsy shops or ebay.
goggle tuteSome places can be pretty expencive but once you have the basics and it's all good quality you can re-use everything and mod it how you want.
If you want steamy style switch the blue and reds for browns creams and whites and add some grease here and there for a more realistic look. And of course stick a couple gears everywhere.
Hope this helps.
P.S Use the interwebs to locate what you need if you cannot find it locally.