I'd like to buy second set of 18" wheels and mount snow tires. I prefer Nokian, Michelin or Blizack, so the combo Tesla offers is out.
Doesn't look like Tesla sells just the wheels. Is OEM from another source the same thing as manufactured by Tesla? What vendor do you like?
There are many companies that sell 18” wheel and tire options for the Model 3. You might want to try Tire Rack, since they are around for a while, pretty large and pretty reputable in terms of companies. I bought a set for over 3k from Tsportsline for my Tesla M3 Performance with the 20” wheels and performance brakes after having 3 blown tires in less than 3 months. The 20” wheels tesla provides are only provided with tires safe for summer use only, as I quickly learned as well. I decided to go with 18” wheels from Tsportsline. The good news has been that the 18” tires are much more durable on roads that I drive on often and I haven’t had a blowout since. The tires they came with are Continental Extreme Contact DWS 06 - 235/45ZXR18s. They are all weather tires and handle the road very well in both warm and cold weather. The handling difference between the 20” that came with the car and the 18” for the average driver like me is negligible. I haven’t noticed any dramatic difference in efficiency either.
The bad news is that 2 of the 4 wheels that I bought from Tsportsline failed. One had a pinhole sized hole that caused a slow leak from day one. I was filling up that tire with air every few days until after going to 4 tire places one found the leak in the wheel. That same place found that one of the other wheels had a crack in it through and through. I was told that a wheel failure was imminent and had to swap it out immediately. Having to swap out 2 of 4 wheels purchased in less than 8 months after they were installed on the car is not acceptable, and I see a few other people have posted to TMC with similar issues after purchasing Tsportsline wheels. I imagine that all of these resellers are outsourcing their wheel manufacture to third parties, but I think there needs to be better quality control, especially with wheels. I was lucky to have been alerted to the issue before I found myself in a dangerous situation and possibly hurt in the process.
The bottom line is that there are options, but do your homework; look online and find out all of the good and bad on any option you are considering. With their batteries, Teslas are heavy vehicles, if substandard materials are used in the manufacture of wheels, they will start failing more quickly and more dangerously than if you are driving a lighter car.