1. Home Depot/Amazon/Harbor Freight
2. Home Depot/Amazon/Harbor Freight
Not sure how else to answer this, so there you go. There's also a ton of resources both here, and on the rest of Google and Youtube that can get you started.
For metal bumpers and skid plate i use 22 gauge steel plate from home depot. Cut them with snipper tool. For cage or sliders i used 3:16 brakeline from autoparts store. You can also get map gas and benzomatic burner from home depot.