It's a simple blood test, done by one of the standard labs. You might need the order from the doc, but a PCP can write it; doesn't necessarily need to be a neuro. Also, MaggieMae is correct; you want the 25 (OH) test. From what I understand, the 1,25 form is pretty difficult to measure, anyway. Also, you're probably already aware of this, but be careful of the units - most here in the U.S. use ng/ml, but our friends up north and elsewhere use nmol/L (32 ng/ml = 80 nmol/L).
By the way, there were news reports recently that Quest had a bunch of errors in their Vitamin D testing.
http://www.nytimes.com/2009/01/08/busin ... btest.html
So, you might want to use Labcorp or someone else.