Can you help me find a car seat for a child that is 40lb? It needs to
have a high back, arm rest, be FAA approved, cup holder and 5-point
internal restraints that will hold 40lbs and up. I can only find
5-point restraints for under 40lbs, But I want more protection than a
lap/shoulder belt restraint.

Where have you looked that you "can only find 5-point restraints for
under 40lbs"?  Every store that I have shopped at for car seats has
versions for up to at least 80 pounds.  You can try any baby store
like Babies R Us, any department store like Sears, or any major
discount store like Wal Mart.

I found plenty of car seats for up to 80lbs. But the 5-point harness
only goes up to 40lbs. After 40lbs you have to use the seat belt.

All of the stores mentioned above and their competitors carry car
seats for up to 80 pounds with the 5 point harness.  I have one in the
back of my car right now.  I have seen similar at every store where I
have shopped for these.

The five point restraints are only good for up to 40 lbs. After that,
it may not be strong enough and you must use the seat belt. Read your
instructions.