Yes, WhatsApp is available for BlackBerry Curve 8530. You can download it by either visiting official WhatsApp website or BlackBerry's app world. So the steps are as follows.
Downloading WhatsApp using App World:
1. Open BlackBerry World app in your device.
2. Search for WhatsApp in search bar.
3. You will get results related to WhatsApp keyword. Click on WhatsApp icon.
4. There you will find green colored 'Install' button. Click on it WhatsApp will downloaded and installed automatically.