The place to begin is requesting your high school records from the high school you attended. Sometimes IQ test scores will be in the record, but as often as not they aren't. Schools typically don't keep records forever. Often anything older than 10 years doesn't exist. If it does still exist, it has to be retrieved from digital media, which can take several weeks. If you know the name of the company that administered the tests and the year they were administered, they may still have the record on digital media. However, they also do not keep records forever. You shouldn't expect to be able to obtain anything older than 10-15 years at the most.
Please let me know if you have questions.
All the best,