There are many online shops that sell auto parts. Amazon.com is one of online shop that sells auto parts for any kind of auto cars. You can visit www.amazon.com
One can cheaply purchase auto parts accessories at any auto part store that advertises cheap products. Discount stores or used stores also are great places to look.
You did not mention where you live so I am unable to do a search to find any auto parts stores nearby. I would suggest you check your local yellow pages for stores near you.
You can find used car parts in Denver at any junk yard, online on craigslist, some auto parts stores also carry used auto parts. You can also bid on them at ebay.
I don't find where any have filed bankruptcy.
Some places will give you a warranty on used auto parts, like auto parts stores that are selling used parts. If you get it from a junk yard though, buy at your own risk.
NAPA Auto Parts located in every state in the country, over 6,000 stores nationwide. Has over 375,000 parts available. NAPA = Never Any Parts Available. Sorry, couldn't help myself.
Sold at any auto parts store, Walmart, Sam's, Sears, and other stores.
Auto body hammers can be purchased at almost any auto parts and tool stores. Sears and Harbor Freight are a couple of places that carry auto body hammers.
Advanced auto parts sells nitrous bottles on their websites. You can also find bottles of nitrous in any auto parts retail store around your neighborhood.
some auto parts stores, like o reilys can get them for you. or they are also in a Hayes manual that can be purchased at any auto store.
Most auto parts stores have wiring kits that you can just plug into your factory wiring without any trouble. Check with your local auto parts dealers
While parts for the Audi A4 are readily available on auto part websites, they are not easy to find at most local auto stores such as Oreilly's or AutoZone. The best local place to look for cheap parts for any car would be local junk yards, an Audi dealership (for used parts) or the local classifieds.