It's probablly because it's not considered a long range cartridge. I personally don't have one, I would love to have one as it is an extremely efficent (sp?) cartridge.
I do however, have three Ackley improved cartridges. One is a .30-06 AI and I'm guessing that the Improved case has about 7% increase over the Standard case (similar to the .30-06AI). That being said, you can start with the maximum loads for any given bullet and increase in 1/2 grain increments. You should see an increase of velocity of 150-200fps over the standard loads when you find a good safe load for your rifle.
Here is a link to Reloaders nest. I've used some of their data to help me find starting points for my rifles.
.338-06 Ackley Improved @ www.reloadersnest.com
Hope this helps.