Bryan,
Johnny is correct that Winchester makes the ammo, but finding someone is the tough part, plus it is expensive. Another alternative is a company called "Ammoman". I have included their website so just click on the work AMMOMAN and it will take youi to their site. It is located in the "Odd Ammo" or "Specialty" section. They sell the Fiocci brand and it does fire, but some Lugers don't operate and eject properly. We all feel it is a little underpowered, but less cost. It is about $20 per box of 50 rounds. This ammo works great in my two .30 cal Lugers, but others say it may not eject 100% of the time.
The only other option I know is to reload. That is what most of us do currently and they work great.
Marvin
AMMOMAN