I bought a B6/B7 S4 MAF (same as B5 RS4) for my build which turned up today. On arrival I saw the previous owner had removed the metal mesh which helps remove turbulence from the air passing over the sensor:
Not ideal but would still suffice. Anyhow, instead of looking for another 90mm housing which I'll have to make some adapters for anyway, I thought about just getting a 100mm housing with the flow straightener built in like this:
Since I don't need the sensor, just the housing, this might be better option that trying to find another one, making up the adapters etc?