PC100 is a very old ram spec. Finding that would be like finding a dinosaur splashing around in your backyard wading pool.
Luckily PC133 is around & should be able to replace, or operate safely with, your PC100 ram with no problems. They fit into the same ram socket.
I doubt you need to go back to Packard Bell for this. You should be able to find some on the web, cheap, somewhere