Shelly, by dashboard cover, I assume you mean a sunscreen or sunshield? You can buy them most anywhere, Target, Walmart, AutoZone.
I bought mine from AutoSport.... www.autosportcatalog.com. It is a customized for the MDX, folds up easily, has UV protection and has a felt backing. Not cheap ($45 or so) but to me it is worth it. Best quality sunscreen I have ever seen. Takes 3-4 weeks for delivery.
We are looking for a carpet like covering for the dashboard to protect it from hot summer sun. We have a similar one on our Honda Accord. It has slots for the defroster vents and it attached to the dashboard with velcro. If you know of anything of this kind please let me know.