The best place to look for RSDesigner symbols is at http://www.rsdesigner.net. In the libraries section (free registration required) you will find pneumatic and hydraulic symbols.
They don't have a full electrical library there just yet, but people are in the process of producing them. The problem is that there are so many standard it's difficult to know what people want.
There are people who are prepared to produce them (for a cost) if you're interested. Again, probably the best place to post is in the forum of http://www.rsdesigner.net because it's just for rsdesigner.