Searching through the archive is extremely easy now.
If you want to search through the entire discourse, you can easily do it by clicking search icon at the top right.
Specific search with a category
You will need to go into the category you wish to search (e.g. CSG1992) and click the same button . In addition to a text box, you will also get a checked box as shown below:
Just search normally.
Same apply to subcategories.
Example search as shown in Rupert’s post