Query to Fill Table - check if value exists?

Dear All,

I have a table with the below structure.  There are 40 districts.  I need to somehow insert a new row for each district associated with the date placing 0 values.  For example the date 1/01/2004 has three rows of data with districts 1, 2 and 3.  The date 1/01/2004 needs to be replicated 37 times for districts 4-40 placing 0 values in Field1.  You'll notice the next date requires different districts to be inserted.

I have no idea how to accompish this.  Please provide suggestions or examples.

Date                District      Field1
1/01/2004       1                10
1/01/2004       2                30
1/01/2004       3                0
2/01/2004       11              10
2/01/2004       12              10
2/01/2004       13              10