Try visiting
Orchid Pests, Orchid Diseases
Look around & you will see information sheets for fungicides, pesticides, etc. You will also see information on recognizing various pest, disease and cultural problems.
One thing to note is that not every fungicide (for example) treats every fungus. So, you have to know which fungus you are treating first. The chemicals listed in the charts on the website might be offered under different trade names in Australia.
I do use pesticides and fungicides, but only very rarely. As you learn to provide good culture, you will find that pest and disease problems do become less common.