There are several brands that sell clay blocks for car detailing purposes. Some of the popular brands include:

1. Marflo
2. Brilliatech  
3. Griot's Garage
4. Chemical Guys
5. Adam's Polishes
6. CarPro
7. Sonax
8. Nanoskin
9. Auto Finesse
10. Clay Magic

These brands offer a range of clay blocks designed to safely and effectively remove contaminants from automotive paint surfaces. Each brand may have variations in formulation, size, and intended use, catering to different preferences and detailing needs. When selecting a clay block, it's essential to consider factors such as the severity of contaminants, ease of use, and compatibility with other detailing products you may use.