Meeting with the principal today and need a quick piece of data. Is there a chart for the WISC-IV that says the occurrence of a particular GAI? Not the percentage, but 1 out of X number of people. I think I have seen a post about it, but I can't find it now.

This one?
http://www.iqcomparisonsite.com/iqtable.aspx

There's some information here, but I'm not sure it is exactly what you are looking for:
http://www.hoagiesgifted.org/highly_profoundly.htm

chay- Thanks! That is what I was looking for. My only question is that the ceiling on the WISC-IV as I understand it is 160. This lists up to 202. Are those scores above 160 because of extended norms?

That is my understanding as well - to get above 160 you need extended norms.

I have had a question about that chart that I haven't seen an answer for. Is that chart only based on FSIQ, or is it still valid for GAI? I would think there would be no difference when GAI is calculated according to the standards, but I have never seen documentation of that.

It is valid for any measure where the mean is 100 and the standard deviation is 15 (or 16).

It has been a looooooong time since I took stats so hopefully someone will correct me if needed but I believe it should apply to any standard bell curve with an SD of 15.

So using the same chart you can figure out that 1/x people have a GAI over a if you use their GAI for a and 1/y people have a FSIQ over b where b==FSIQ. For kids with very different GAI and FSIQ (a & b) you could have very different x and y values.

too slow

GAI is different than FSIQ, and is discussed on old threads including this post with links to other sources of information.