What is a good way to find a doctor to test my stepson , please read?

this goes with my other question, my 5 year old stepson does not live with us but will be with us for 3 weeks this summer and we feel strongly that he needs to be tested for some problems, but he is 3 hours away and he doesnt have a doctor here, he is on medicaid with his mother as far as we know, but i have no idea where to start? we are in central IL . how do i find a doctor that will test him, and that will except medicad, and how soon should i make the apointment since he wont be here until the end of June i really have no idea where to start and i really need some suggestions!