Guild stores or writ vouchers (obtained through doing master crafting writs).
I can't find it i can only find a couple pieces
Ask in zone or guild chat if anyone is willing to buy the entire Ebony motif book (costs 300 writ vouchers - best value because buying it page by page costs 350 writ vouchers) and if they would then sell it to you for gold. Or buy master writs you have the skill/knowledge to do that add up to 300+ writ vouchers. Then you could complete master writs, get vouchers, and buy Ebony motif book yourself.