First, rangers themselves make some fine bows once high enough level. But, if you're looking for something more useful yet easy to acquire, a Blackwater ranger, Silverwood Forest has someone with a Bow, Emerald forest has multiple but one of shivering ivory, some hunters near the Underdark entry near Arendyl, and a ranger hiding in the Weald, each has a non-physical component to them; light, cold, acid or poison. Similarly, a ranger from Balator as well as someone inside the Black Dragon's lair both have non-physical elements but are much more difficult to attain. The High Lord's keep has a hunter and there are some roaming Eil Shaeria as well as the Siege Encampment. Some of these bows are either anti-good or anti-evil, and there are a few race dependent bows like the one from the guild in Arial city. If you don't have the area knowledge, just ask a few people IC, maybe you'll get lucky.