First of all, 500 score, not 150.
Second of all, with a good bronze grinder, it's easy to get any rare you need within decent speed.
Third of all, no good deck ever uses 4-6 arsenics, except possibly deathstalls, which are rather rare and unheard of.
Flying weapon arsenics just pales in comparison to a monodeath, and monodeath rushes only use 2-3.
To get to 500 score easily, grind AI3 with a decent AI3 grinder. You can find some examples
here. I personally recommend the nymph tears rush.
To get rares easily, grind bronze arena. I recommend a modified nymph tears rush or a monodarkness to do this.