I've seen it notes on other pages that the level 48s are the ones to go for. The folks that posted there said the 48s have an 80% drop rate, while the 47s have a 25% drop rate. It seems accurate from the few I've farmed so far.
The best place to get these considering you can only get a few from Urugarth is in Dolroth off the Deadly-fire Drakes. These same Drakes are a part of the [48] Scaled Menace quest.
The best spot I have found if you are going to solo them is 0.6S, 21.0W behind one of the nests with eggs. Safe place to afk at as well as the paths never cross that location. I was able to get most of my 25 scales there.