Logic 7.0 can handle up to 253 fonts. This refers to the total of fonts in the System and user Font folders. The fonts are loaded in alphabetical order, and no fonts after number 253 will be available.
Click here for more information on Font locations.
This issue is resolved in Logic Pro/Express 7.1, because there is no longer a limit on the number of fonts Logic can use.
Regardless of the Logic issue, you might also consider managing your fonts with a utility such as Font Book or third-party font management software.
Before upgrading to Logic 7.1, another workaround is to create a new user account for working with Logic, making sure the total number of fonts for this user is less than 253.