Got 4 Red lvl 100 dragons here today. Still 4 lvl 100 dragons short, since I have both a 5* and a 6* that might reach evolvable state during the week, but I guess I'll settle for just evolving the 5* then..
And yes, I like to aquire my dragons in advance, before my knights reach max level. So I generally keep 3 lvl 100 dragons, 5 lvl 20 dragons and 5 lvl 5 dragons in storage for each color. Occasionaly failing to maintain stock is less frustrating than failing to get the dragons you want to use immediately. Requires a LOT of room for girls/dragons/manyus though, my maximum storage is 175 right now, so that was a 25 flower gem investment.

You just have extremely shitty luck. Whenever I decide to farm dragons, I always have at least one run out of four with multiple golds.

Its luck of the draw. Earlier on last week I scooped up eight gold dragons with 350 Stamina, today with blue dragons and same amount of stamina, nothing. Just a bunch of baby dragons with their infuriating, crappy faces