Aren't filters the same as plug-ins? I think so! If you search for plug-ins you will find a ton.

Here's a link - I hope it works:
http://graphicssoft.tqn.com/cs/paintshoppro/
It also had a tutorial how to install the plug-ins.

Another link:
http://showcase.netins.net/web/wolf359/plugins.htm

and the last:
http://www.putertutor.net/paint/morestuf.htm

I installed a few I downloaded (for free - but I don't remember where) and here are the names (might make it easier to find):
Eye Candy 3.1
Almathera
Graphics Plus
Xenofex 1.0

Usually Photoshop plug-ins work for Paint Shop Pro too! If you need help, contact me.

Good luck

Ivonne