I'm skimming quickly through the Leather set effects on jDnF/Arad Senki Wiki at the moment and listing whatever attack speed increases I find.
Burning Rider full set offers a +3% attack speed increase along with movement speed +2%, though it's low-leveled at 20-25, so it gets useless at your level.
There's the two-piece Behemoth sets at 25-30, two different sets and you can equip both sets.
at 35-40, there's some kind of "Asarutoatakka" set that gives +1% attack speed, but multiple skill increases for Rangers.
Interestingly, the Spitfire set at 35-40, something along the lines of Million Deadshot set's shoulder gives +3% attack speed. Battle Mage's Shadow Veil set shoulders also give +3% attack speed.
"Andafutto" two-piece set gives a +2% attack speed increase, and one of the sets don't use shoulder, meaning you can stack with the +3% shoulders, or even do both sets and get +4% total.
Anything after that is 40+. QQ