I was able to buy a set of two NOS Campi cyclocross chain guards for about $40 plus shipping 3-4 years ago on ebay, and have seen 1-2 similar listings on ebay since then.
They are a nice item to have on my UO-18 mixte commute bike, as they keep some of the chain grease off of my pants.
You might also check with American Cyclery if you're in San Francisco some time. They have a wonderful collection of vintage components that they might show you if you ask.
Billy's suggestion will work, but it takes much more work and skill than I currently possess. I'd have to be really desperate to take on that kind of project.
Jon Spangler Alameda, CA USA
On Feb 7, 2009, at 4:03 PM, <firstname.lastname@example.org>
> Message: 11
> Date: Sat, 7 Feb 2009 23:18:25 +0000
> From: <email@example.com>
> Subject: Re: [CR] Chainguard for 144 bcd.
> To: <firstname.lastname@example.org>
> Content-Type: text/plain; charset="utf-8"
> Hi all. Campy made an inner and outer chainguard for a cyclocrtoss
> setup. The inner one would mount on the spider arm. But it's not
> hard to take a used, sharkfinned 144bcd chainring and cut the worn
> teeth off to make a chainguard. I've done it and i'll post a pic
> tomorrow. The ring should be about 6-8 teeth bigger than the ring
> you want to use. Billy Ketchum; Chicago [where it's 50 degrees F.
> and the snowpack is melting and i rode 30 miles today], IL; USA.