Generally, I don't search DataTables: I tend to filter DataViews instead.
Assuming you are using a DataGridView, create a class level DataView using the DataTable as it's source and use the DataView as the DataSource of the DGV:
private DataView dvBooks = new DataView();
...
DataTable dt = myList.ToDataTable();
dvBooks = new DataView(dt);
dgvBooks.DataSource = dvBooks;
Then use the RowFilter property to filter the displayed rows:
dgvBooks.RowFilter = "[date] LIKE '%-" + monthNumber.ToString("D2") + "T%'";
The system will only show matching records.