Dynamically changing tables in datasource in SSRS
Given that you expect the number of data sets to grow over time, your best bet would be to create a stored procedure in the database that uses a parameter value to determine the source tables and dynamic SQL to build the query.

Create an SSRS parameter to match and pass this value through to the data set and the stored procedure will return the results from the table specified in the parameter.

Basic Example:

CREATE PROCEDURE spGetData
(
    @SourceTable NVARCHAR(255)
)
AS
BEGIN

    DECLARE @SQL NVARCHAR(MAX)

    SET @SQL = 'SELECT [Column1], [Column2], [Column3]
    FROM [dbo].[' + @SourceTable + '_Audit]'

    EXEC sp_executesql @SQL
END