Implement a string indexer or a method to get column by unique name in RadGantt. 

Example  of string indexer
//
// Summary: This class represents collection of Telerik.Web.UI.GanttBoundColumn.
//
public class ColumnCollection : BaseCollection<GanttBoundColumn>
{
	public ColumnCollection(){...}
	public ColumnCollection(IGantt owner){...}
	
	public GanttBoundColumn this[string ColumnName]
	{
	   //considering columnCollection is internal variable holding list of columns.
		return columnCollection.Where(c => c.UniqueName == ColumnName).FirstOrDefault();
	}
}

Example of a method can be similar to RadGrid's GetColumn and GetColumnSafe methods: https://docs.telerik.com/devtools/aspnet-ajax/controls/grid/how-to/Common/using-the--getitems-getcolumn-and-getcolumnsafe-methods.