You want one from a longitudinal engine'd 1.8t car, i.e. A4 or Passat. There's a variety of different trims, but the K03-005 is the most commonly available. K03-029 has a larger turbine wheel (so the boost threshold is higher, but it'll flow a bit better), and the rarer K03-073 is a -029 with a larger compressor wheel and housing - very similar to a K04-015.
Having tried all the aforementioned K03 trims, I'd recommend the -029 though the -073 is the way to go if you want to break 200bhp.