I don't see how the good schools guide or any website can have all the info - as others say catchments vary from year to year, depending on how many siblings and SN children are taking places. Then add in the credit crunch which has made demand for places at decent schools way higher than previously.
For example, last year my dcs' school which is lovely and Ofsted "good with outstanding features" had a catchment that was basically open ended as we live in a wealthy area where many children go private. Everyone who applied got in.
This year, the child farthest away (without a sibling) to get in was 300m. Tons of people were left without any school place at all.I believe some LEAs do operate "fixed" catchments but they're an exception.
So be very careful about buying a house on the basis of it being in a "catchment". For a popular school, unless you are virtually opposite the school gates you may still get squeezed out.