Coincidently I talked with Zise about this a while back and he already explained why this is not possible. We can't add fonts to the forums. Fonts are read by your own PC, not Vbulletin. As practically everyone by default has fonts like Arial, Century Gothic and all the Word fonts installed on his PC, they all work on Vbulletin if you use the font-tags with the name of the font even if they are not listed in the font drop down menu.
I even tested this. I installed a series of wacky custom fonts I downloaded from the internet on my PC. Result? They all work on NB, I can see those custom fonts because my PC can read them, I only need to add the font name to the standard font-tags and voilá. The problem with that is that only the people who have downloaded and installed that same font will be able to see it. Everyone else would just see the standard font.
So in theory if you could get everyone on NB to download and install a custom font, then you could use a custom font that everyone would be able to see.