The wife's VRS is making a moaning noise at certain speeds and I'm guessing it's wheel bearings, have recently changed all the brakes and the front tyres too, but no change.

Firstly, how easy is it to diagnose noisy wheel bearings?

Secondly, is there another source of them other than VAG as they ain't cheap and I'm assuming you need a special tool?

Any advice welcome!

Bearing comes complete with the bearing carrier, hence the price. Special tools are needed to fit new assembly, as all the force has to be applied to the bearing only and NOT the hub. It can be done DIY, but you need to know how. Lump hammer, large vice, and suitable socket to act as a bearing press. Hard to diagnose in early state of failure, as simply jacking up and rotating wheel, all usually appears to be ok. They tend to start failing at 60,000 miles.

are you sure its not just tyre noise, Contis and especially Bridgestones can be very noisy when they getting low