If you have special fonts available (or if some fonts are unavailable) at your site then you may need to produce customised versions of the font definition files; these have extension .fd and are read by LaTeX to obtain information about the font files installed at your system and when to load them.
Although we do not encourage such customisation, you will find information about the content of these files and its syntax in the documented source file cmfonts.fdd and LaTeX2e font selection in the file fntguide.tex. [We hope to be able to provide further information and examples on this subject at some time in the future.]
Please note that the use of customised font definition files has the following consequences.