With Heatran I've been really lucky already. As for Giratina and Cresselia it took me quite some time and trades to get them Lucky. Heatran on the other hand I was able to get Lucky from my 2nd trade already after catching my 3rd Heatran! That was really awesome and unexpected.
I've been trading some Delibird as well as I would like to try and get a 100% IV. The trades give that extra chance by rerolling the stats so I love trading most Delibird that I catch. And I've been able to get that one Lucky already too!
Have you been catching some Delibird as well? Any luck on finding a Shiny?