Abs for ectomorph types?

I am 23, 78kg, generally fit the ectomorph profile but I am not as skinny as when I was younger for example.
 
My abs are there, but are *just* hidden a little.  While it's easy to find bodybuilding routines for everything else, for some reason really good ab routines are less common.  Can someone recommend one that really worked for them?  I guess something with weight training probably helps...

How tall are you? around 6ft? You probably have low bodyfat as it is, most people would tell you to focus on diet and tell you that everyone has abs.
 
What I'd suggest is combing a cleaner diet with a decent workout regime and see how that goes. Try and cut down on sugar and saturated fats.
 
As for exercises, the big compound movements like deadlifts, squats, OHP, bench press, dips and chin ups will all engage the core muscles. To hit the abs more directly, you could try something like squats supersetted with crunches, followed by leg or knee raisers.
 
Here's a little circuit I did the other day, all 20 reps, did the circuit 3 times with a minute or two rest inbetween.
 
Ab crunch machine set at a weight where you can just manage 20 reps.
Regular crunches.
Knee Raisers.
Machine Oblique Twists.
 
My abs and obliques are still aching and it's 2 days after I did them...
 
Focus on contracting the abs when doing the exercises instead of just going through the motions.
 
Hope this helps.

sort out diet and cardio,training
 
but abs routine is not nesserly needed for abs i do the following by doing compound the i do 1 part of my abs a day
 
plank-kettlebell swing - upper abs tagerted
 
also do loads of compound moves chest,back,legs all work abs but i noticed leg moves such as deadlift,romainian dealift,over head squat target them very well
 
side planks - side rope crunches - side abs target
 
leg rasie-leg hold-reverse crunches-leg hold - swiss ball leg tuck -lower abs target
 
uneven suitcase walk - target abs stabillitly

If your doing a lot of compounds already which use your core I'd just add in a abs session on your last session of the week.