There are plenty of conservative atheists. I'm one of them. But the main reason that you don't hear much from them is that they tend to not speak up about being conservative.
As most of them discover, admitting to being a conservative among atheists is a very dangerous thing. It's like admitting to being Jewish at a KKK meeting; the amount of hostility directed at you from other atheists is utterly incredible.
I've attended meetings of atheist groups locally, and given their reaction to my statement that i was a conservative, I think that I probably would have gotten more acceptance had I said that I was a child molester. Some people were so upset that they got up and left. Others looked like they wanted to assault me then and there. Most were openly hostile and a couple told me I wasn't welcome there. There was absolutely no attempt to understand my point of view or be inclusive; the place was basically treated as being a liberal club, and anyone with different political opinions was the enemy.
By contrast, I have gone to conservative religious groups, and announced that I was an atheist, and the reactions ranged from nonchalance to puzzlement to pity, but no one had anything averse to say, or treated me badly in any way. One or two people talked to me about why I was an atheist, but no one was ever impolite or tried to make me feel unwelcome. On the contrary, many specifically said that they would like to see me come back, and that they wanted to be as inclusive as possible, regardless of personal differences. There was no attempt made to convert me; they were just glad to have anybody who was a conservative, no matter what their faith or lack thereof. They were conservatives first, and religious second, and did a good job of keeping any personal feelings private.
So the bottom line is that I would expect that most atheists who are conservative in outlook probably have learned to keep their political opinions to themselves around liberal folks, and they undoubtedly find a much more welcoming environment around other conservatives than with fellow atheists.
I should add that I've found the same thing to be true here. The amount of hostility towards conservatives by many of the people here totally swamps out any shred of commonality we might have as atheists, and makes me feel quite unwelcome. This is one reason I rarely visit here.
Frankly, we as atheists are too few in number to be able to afford the luxury of having a political litmus test for membership. If we are to have a chance of standing together against religion, we need to be able to put aside political differences and unite for a common goal. This is a lesson that religious groups have learned, that atheists have not, and if we want to be able to make any headway in this society, we need to stop creating artificial divisions among ourselves over disagreements unrelated to our focus.
However, based on our history, I think that's unlikely to happen any time soon. Sadly.
I am a moderate Democrat but I consider myself as someone who leans to the right on such issues such as illegal immigration, foreign policy, and keeping our homeland safe and going after terrorists and rogue regimes. I admire Christopher Hitchens for his stances and being on the right side of history time and time again. I find many atheists (especially those dogmatic leftists) tend to not be rational but irrational: I always use the slogan: "I think with my own brain on issues" rather than being a political ideologue. I find that sentiment to always work very well.
BTW: I admire President Bush for his foreign policy objectives - although Iraq was a mistake as he should have gone to Iran instead, the world is a better place without Saddam Hussein and the international community is a better and more secure place than it was a decade ago.