It doesn't exist. You can do 2H weapons up to +25 agi with little effort on Timbermaw rep, 1H weapons up to +15 agi with more Timbermaw rep, boots up to +7 agi, gloves up to +15 agi if you have the crystals and the formula (+7 agi is normally what people go for) and cloak up to +3 agi.
I've never seen or heard of any agility enchant to bracers. In fact it would be at odds with the enchanting style of things if such a thing existed. Bracers tend to be the cheaper enchants to learn and the formulas drop more often. These are generally +stam or +deflection (there is the odd +healing and +int formula).