I've noticed here in DC that museum floor plans are rarely available on site at the moment. I guess it's a COVID safety precaution, or maybe it's partly financial. In any case, you can't count on picking up something that will help you navigate the building (or the National Arboretum, for that matter). I see there's a similar notice on the website for the Accademia in Venice. There's a nice downloadable map you can either put on your smartphone or print out and take with you.
If you're headed to any large museums this year and like to have something to help you navigate, I recommend checking the websites for floor plans and other useful information you might normally expect to find on handouts.
Note also that free-admission periods may have gone by the boards, at least temporarily, At this time the Accademia in Venice has suspended its practice of offering free admission on the first Sunday of the month.