Fret no more! You'll find piles of them in greater rift rank 1. I used to run out of Topaz, veiled crystals, and arcane dust constantly, but since the recent post about gr1 speed runs I've been building up my stock much faster than before. With a well geared, properly spec'd character you can clear a gr1 in 3-4 minutes, and you can finish at least 15 in an hour with ease. I usually find about 30+ crystals & dusts, and 2+ of each gem per run. Torment legendaries can also drop, so you're not missing anything by playing this super easy content. If you're having trouble farming gems or mats, give gr1's a shot.