insideevs.com tracks tesla sales and has a pretty good track record on accuracy. I think they call dealers for info and make a prediction. last year (according to them) they had to correct Model S by only 400-500 units.
And don't believe the BS, Tesla doesn't release numbers because they want to control the media story. Even their quarterly numbers are heavily manipulated and inconsistent on what is released. If you are curious, the next 2 quarters are going to be interesting. Model S demand is falling (or not actually supply limited, and unable to grow to target), and the 25,000 Model X reservations seem to have evaporated...you can order a Model X now with roughly the standard lead time despite them delivering <10k units ever.
It's going to be a tough 12 months ahead.