You could try any Ducati dealer. If you look in the parts catalogue on ducati.com, you'll see that all the stickers have a part number.
They're not the sort of thing that dealers would have sitting around on shelves though. They'll need to be ordered and could take ages so you might want to try eBay. They have sticker kits on there all the time, you might find what you're looking for. Some of the eBay sticker shops advertise a 'design your own' service so they might come up with what you're looking for.
Final alternative is to try and copy the font and logo using some sort of graphics package. I think that the fonts that Ducati use are Univers Extra Black for the bold 'Ducati' typeface and Univers 45 Light for the skinny font. Both fonts look italic, but if you use the italic font it's too much. So if you can, use a graphics package that can skew the letters to the right by 12 degrees. If you can make up the logo like that you should be able to find a local signwriter to cut you some sticky vinyl of the right colour. stick it on and lacquer it over.
After all that theory, I've been trying to get the same for my ST for ages and haven't managed it yet...so you might just want to ignore everything I've said
Alternatively