Most schools would be able to put you in touch with some of the regular grind instructors in the area, but it's not a required service so never guaranteed.
Other possibilities (if the web site doesn't work out) are asking other parents in the area (some will have had children do grinds and may have first hand experience), contact teachers directly (either from the school or from a nearby area who teach at another school) [most teachers in the school I went to did give grinds in the evenings, even if they don't when approached they may accept] or looking for members of your family who may be able to help (I've given grinds in Physics, Maths and Tech Graphics more than once to family members [they must have been desperate]).