Check around with the folks who sell the old software, such as B&R Computer, Herb's Mac Stuff, etc. I don't think either has it in inventory right now but it wouldn't hurt to ask.
If you look on eBay, make sure you look for a FLOPPY version. There are usually tons of CDs of Carmen on there but they are too new.
Don't forget the local sources like school surplus, thrift stores, used bookstores, etc. Plus disks occasionally will show up randomly here in the trading post--remember that big lot Mike had a few weeks ago?
The big trick is that you also need the Brøderbund edition of the New American Desk Encyclopedia along with the disks. If you find disks by themselves, you may want to look at a library book sale or a used book store for this.
Drew: Do you realize that your signature contains two alternate names for the MacMag virus???