Mushrooms and vitamin D from Easy Immune Health
from internet Feb 2010  http://www.easy-immune-health.com/Vitamin-D-Foods.html 
Mushrooms, like us, photosynthesize Vitamin D from the sun.
Unfortunately, farmed mushrooms are grown in the dark.
Wild mushrooms, however get some sun exposure and have a certain amount of Vitamin D. A study done on volunteers who ate wild mushrooms every day at lunch for 3 weeks showed that this Vitamin D gets absorbed and so is actually one of the few very good Vitamin D foods, and the only natural source of Vegan Vitamin D.
How much Vitamin D do mushrooms have?
Wild mushrooms have about 400 - 500 IU per serving.
Pretty soon, however, you may see Supermushrooms in the supermarket. These will be mushrooms that have been exposed to UV light either during or after harvest.
These mushrooms may have up to 2500 IU's per serving! Wow!
If you can find sun dried mushrooms, this would be another great source of Vitamin D. If you can't get wild or sun dried mushrooms and don't want to wait for Supermushrooms, theoretically you should be able to make your own Supermushrooms by sitting store bought mushrooms out in the sun or under a UV light for 5 to 10 minutes!
The downside to getting your Vitamin D from mushrooms is that they only contain Vitamin D2- and Vitamin D2 is a much inferior form to the Vitamin D3 that is made in our own bodies from the sun. Therefore, mushrooms are not the recommended way to get your vitamin d. If you are a vegan or vegetarian, then take a look at the Vegan Vitamin D page and find out what your best options are.
So as you can see, there are not many good sources of Vitamin D foods. Really the best and cheapest source is mild exposure to sunlight on a regular basis.
If this isn't possible, you may want to consider getting your Vitamin D level checked and supplementing accordingly because getting your requirements through Vitamin D foods may not be realistic.