Here in Illinois there are a few places you can turn to find advocates. When making an IEP for school generally the parents and teachers get together to discuss goals and set up supports and services for the year. Parents can also call meetings throughout the year if anything may need to be revised. The school will ask the parents to sign the IEP to agree to the changes. Advocates can attend the meeting at the request of the caregiver. Their place in the meeting is to help the parent advocate for what their student needs.
Resources for find an advocate in Illinois:
Additionally an abstract about the benefits of an advocate can be found at https://experts.illinois.edu in publications -The efficacy and impact of a special education legislative advocate