The biggest manufacturer of Oxidized Bitumen is Iran 

Iran producing largest quantity of oxidized bitumen in various grades as below:

Blown bitumen grades or Oxidized Bitumen are produced by passing air through the penetration grades. This process gives the bitumen more rubbery properties than its original formula and they are simply harder bitumen. 

Oxidized bitumen 75/25

Oxidized bitumen 85/25

Oxidized bitumen 95/25

Oxidized bitumen 90/40

Also medium grade oxidized bitumen 90/10

Oxidized bitumen 90/15 and hard grade including

Blown bitumen 115/15

Oxidized bitumen 110/15

Oxidized bitumen 105/5

Oxidized bitumen 105/15

Oxidized bitumen 105/35

Oxidized bitumen 150/5 , ...

Iran blown asphalt is high quality and economy compare other countries since oil price in Iran is cheaper and a lot of manufacturer producing air blown asphalt.