Amazon offers Celox Grout Cleaner Scrub Brush for +Eligible for Free Super Saver Shipping. 

Product Description:
V-Shape Grout Cleaning Brush - CELOX grout cleaning brush with large V-type stiff bristles can enter those hard-to-reach corners, ground cracks, concrete floor, kitchens and bathrooms tiles floor, narrow spaces at any Angle. A stiff brush easily removes stubborn dirt or grime.