I was wondering if there were any sample placement tests that I could give to my son who is currently in 7th grade homeschool.
For what subjects?
Curriculums are so varied, that I doubt if you'll find placement tests.
What does your home school advisor recommend?
The equivalent tests for all subjects, math, english, science, social studies
The purpose of these tests is to find what curricula will best help your son. Please don't push him into practice tests. You need to find out where he is now.
How can you find out where he is now without testing him? He will have to take the tests when he starts public school anyway, we just want to make sure he is ready so they don't hold him back a grade or two.
You can't find out where he is without testing him in some way or another.
If you've followed an effective home-school program, then your son should be ready for an equivalent public school program. The important thing is that your son be placed in a program where he can be comfortable and experience success.
Most schools attempt to place a student with others near his age. If his skills are signifantly below others, then the school might recommend a special education program.