You can easily use the RadGrid's client-side API to achieve the functionality you desire. Here is an example of how you might create a JavaScript method that would take a column name and return that column's index:
function getColumnIndexByUniqueName(columnName) {
var masterTableView = $find('<%= RadGrid1.ClientID %>').get_masterTableView();
var column = masterTableView.getColumnByUniqueName(columnName);
var element = column.get_element();
return element.cellIndex;
}
I hope that helps. Let me know if you have any further questions.