i only eat steamed broccoli (15min for the stalks and 4min for the greens), and the frozen variety never has the familiar "crunch". Maybe I tried only bad quality frozen stock.
Freezing breaks down cell walls (ice crystals form and puncture cell walls, faster freezer leads to smaller ice crystals leads to less breakdown). I'm not an expert but I suspect you may never get the crunch from frozen broccoli.