I've got two plates from the Christmas 1990 Madonna and child collection.. How do I find out what they're worth?

You might check with your local arts/antiques dealers. They are generally best equipped to answer these kinds of inquiries. The NGA would not be in a position to know their value. Someone else said eBay, that's typically a good indicator of their value (if you can find a significant sample of similar products).

The museum doesnt do that.