Korean BBQ in Yonge/Sheppard area
Authentic KBBQ is mostly around Yonge and Steeles area, my favorite ones are Seoul House and another place at Yonge and Clark (really quality food, BBQed with charcoal; unfortunately I don't remember the name, maybe someone can chime in). There are a few near Yonge/Finch. I presume you've searched around for these other areas.
I'm not aware of any around Sheppard.
Here's a few, with links from previous posts about what is good to have at each place:
Sariwon for the BBQ (not sure if they do Charcoal BBQ vs regular gas)
Oh Geul Boh Geul
If you want to try Charcoal BBQ, go to Seoul House near Yorkdale Mall.
If you're looking for the all you can eat ones, the meat quality won't be nearly as good.