A rock hit my windshield and caused a 12" crack on the right side. Tesla insurance was quick to refer me to the nearest service center, and the front windshield was replaced within a week. It was an overnight install, and I got Uber voucher to get home. Note that this was a few months back so I assume parts were less of a problem. I suggest you calling up all the Tesla service centers in your area and see if anyone has them in stock. Though if the crack isn't too distracting, it's not a big deal as the inside layer of your windshield is still intact.
The cost was $980. I paid the $100 deductible and Tesla Insurance mailed me a check to cover the cost. There are cameras and sensors on the windshield, so I doubt that there are generic windshields available.
The kicker is, the next day after picking up my Model 3, I was driving along the freeway and someone decided to abort taking an exit, kicking up dirt and stones, and one ended up hitting my brand new windshield, causing a 1/2" crack on the driver's side. Insurance covered the $80 repair cost, but now there's a bulge where the crack was, causing a lensing effect. I can't believe my luck.