Overhead Door Atrium Door Latch

I have an Overhead Door Atrium Patio Door that the latch mechanism requires repair.  The handle flops up and down and barely engages the latching mechanism into the door jam.  Feels like a spring might be broken. The door was installed around 2002. Any thoughts on repairs/replacement parts availability would be most appreciated.  I contacted dealer but at this time they are unsure if they can find replacement parts. They will get back to me.
 
thanks