That is a RS3 bumper I got off eBay Germany for £400 . I originally wanted an S3 one but the seller offered me an RS3 one painted in Ibis White for £20 more .The gloss black diffuser suits a white car far better than the dark grey S3 one in my opinion .
If you want to fit this on a 3 door you would have to get the top section what is really easy to find and then just get the RS3 lower section . The link above shows an even easier method to getting something that looks similar .
I do not recommend modyfying the parts to fit a 3 door, You have to butcher a oem rs3 diffusser and a oem lower 2011 s3 bumper which only fits a 2011 oem s3 upper bumper. It involves allot of hand shaping and fettling. One wrong move and you have thown money out the window! You also need to fabricate new hangers and brackets because you will have cut off all the standard ones. 80mm tips look lost in a rs3 diffuser so that needs addressing also. I am pleased with the results on mine but I would never ever do it again!
The problem with the cheap solution in the above ebay link is the rear wheel arches, that bumper will not line up with a3 or s3 wheel arches without modification.