Questions that might help with the naming:

- Are you servicing a specific region (don't say "No! ANYWHERE IN THE WORLD!", cos not even Amazon manages that)?

- Who are your primary customers going to be? You say mechanics, but are they the only customers possible?

- Does it have to be something with "Auto Supplies" in it? Think of successful sites whose names don't have anything in common with the actual purpose of the site (Google, Yahoo, Zillow...)

- Maybe use your own name to cater to the customer segment that goes for the ol' folksy crap, eg. "Miller's AutoSupplies", "Jefferson Auto Wares" etc.