Usually, your local region also hosts regional science fairs in order to qualify for ISEF. If you are interested in the Intel STS, here's a link-http://sciserv.org/sts/
Keep in mind that Intel STS does have restrictions on age, grade, etc.
You can also look into local colleges and universities which often host high-school and middle-school fairs as well, be sure to check with your teacher too!
Hope this helps!
"There is a single light of science, and to brighten it anywhere is to brighten it everywhere." -Isaac Asimov