We want to go to the museum today. Tried to buy tickets online. But it showed “no availability”for today. Can we still go directly to the museum and Wait in line to purchase the tickets there.

Yes you can go you need to wait a little bit but is available

I just went and believe people were there to get tickets on site. Also you may want to check Groupon. You might also get a better deal.

Definitely check Groupon. It's a great deal that we used when we went!