Assuming you have a date field in your Viz, you may be able to use "Show Empty Rows" or "Show Empty Columns" under the Analysis... Table Layout menu.
Without a packaged workbook, it is difficult to recommend a solution for your specific use case.
Try this work around:
I will explain this scenario using sample super store data:
1. create a calculated filed with this formula (ZN(Lookup(Sum([sales]),0))
name it as lookup with ZN
Now you want the cells without data with "0" right.
1. drop category filed into columns
2.create a duplicate for catgeory filed in data pane
3. drag the duplicated filed into rows
4.Now drag the "lookup with ZN" calculated filed which you created in first filed to text. now you see that the empty cells are populated with zero.
This solution works where there is at least one value in a row or column, however I think what OP is asking is how to get Tableau to 'pad' data into a row where there are no common values.
I'm having the same issue and trying to solve it in Tableau without writing SQL joins. I'll keep searching and trying a few things... will report back if I find a solution.