Ideas:
1-google something like "educational psychologist [insert your metro area]"
2-If you have a state gifted association go on their website to see if they have a list, or contact them.
3-If you live near a larger university or can drive to one, a test like that could be given by a graduate student for a reduced fee.
Call them and ask if they give that test, that they have some solid experience with children of your child's age range, and only pursue if they sound like they really know what they're talking about.