It really isn't hard to find genes for intelligence - assuming that you mean the conventional thing by "a gene for x":
"Maynard Smith reached for a hypothetical example and came up with a 'gene for skill in tying shoelaces'. Pandemonium broke loose at this rampant genetic determinism! The air was thick with the unmistakable sound of worst suspicions being gleefully confirmed. Delightfully sceptical cries drowned the quiet and patient explanation of just what a modest claim is being made whenever one postulates a gene for, say, skill in tying shoelaces.'"
One example:
"Gene found for mental retardation"
Yes, it is very hard. I know, because I know people attempting to find those genes. They report that it's very hard. I specifically said normal variation in IQ to make it clear that I'm not talking about mutations and variants which cause retardation. Those QTLs of large effect are easy to find, but they aren't implicated in normal human variation. How do we know this? Because they don't show up in linkage or association studies consistently.
I didn't say it's impossible. There were many things impossible 10 years ago that are possible now. But I didn't make that assertion in ignorance.
Link.
"Razib Khan has an academic background in the biological sciences, and has worked for many years in software. He is an Unz Foundation Junior Fellow. He lives in the western United States."
Razib's writings can be found on his blog, Gene Expression.