"But Black couldn't have bought a Firebolt! He's on the run! The whole country's on the lookout for him! How could he just walk into Quality Quidditch Supplies and buy a broomstick?"
-- Oliver Wood (PA12)
Quality Quidditch Supplies was Harry Potter’s favorite shop in Diagon Alley. He visited it often when he stayed for three weeks at the Leaky Cauldron, since that summer the new Firebolt racing broom had been introduced and the shop had one on display (PA4). Quality Quidditch Supplies also once displayed a full set of Chudley Cannons robes in the front window (CS4).
From the Web
Harry Potter Wiki: Quality Quidditch Supplies