Amazon.com : Toothbrush Replacement Heads Compatible with Philips Sonicare, Medium to Soft Electric Brush Head Refills for Sonic Care DiamondClean C1 C2 C3 G2 G3 W2 W3 4100 5100 6100 etc, 8
Best Buy: Philips Sonicare C1 ProResults Standard Replacement Toothbrush Heads (3-Pack) White HX6013/63
Amazon.com : Toothbrush Replacement Heads Compatible with Philips Sonicare, Medium to Soft Electric Brush Head Refills for Sonic Care DiamondClean C1 C2 C3 G2 G3 W2 W3 4100 5100 6100 etc, 8