Are they not appearing in the list?
You need to add the correct FGD to your Hammer configuration:
Gives you access to ALL the entity types in CS. Unzip everything to your Hammer/fgd/counter-strike folder and tell Hammer to use the new FGD (Tools->Options->Game Configurations->Game Data Files box).
Or: You haven't even got to the list?
Click the lightbulb.