You can find datasheets for trans cores as above, however when you put an airgap in the core info for all the changes it makes it often not readily available.
What is it your trying to do, build a flyback trans or a push pull?, I've messed with these things a fair bit.
With a bit of patience you can re-use ferrites from dead equipment, the more important parameters can be measured fairly easily.
Edit: Just occured to me if its a trans in a particular design you need you'll only get that info from the manufact as they will have developed the design, there are very few pre made ones.