I've bought them before but they do take a few weeks to make/ship. I have an unused one on hand if you'd want it asap. Just PM me if you want it sooner.
Tesla still has some. Just call your SC and have them see if they are still available.
I just asked for one last week. It arrived at the Houston North SC yesterday. I think they said they still have a few available to send out from Fremont.
As I noted before....the one I just got from Tesla was in fact a TRUE Tesla branded cover. I was told they still have some left. Just call your local service center and ask for parts. They should be able to acquire it for you.