Some external drives I found:
https://goo.gl/DsFjFj (not blu-ray, but has 4 star rating on amazon)
Some blu-ray ones: (More Expensive)
https://goo.gl/1gHiGW (3.5 star rating)
https://goo.gl/s1HLrs (has USB 3.0 and 4 star ratings)
I don't really know what makes a drive good but I just found a best external drives page and listed a few.