The Elder Scrolls III: Morrowind

I don't know an exact location to buy one, but if you just want one then open up the console (with the ~ key, next to the 1 key) and type in EXACTLY this (with the quotations, otherwise it won't work)

player -> additem "bonemold long bow" 1

That's the word player, one space, a dash immediately followed by the little greater than sign, a space, the word additem, a space, the words "bonemold long bow" in quotations, a space, and then 1. Easy.

There is one in the smuggler cave Beshara, which is east of Vivec City. The person holding it is a wood elf.
Killing the smugglers is part of the Angry Trader side quest.

You can get one from Alusaron Blacksmith. His shop is at the top floor of Vivec, Foreign Quarter.

The easiest one to get is from one of the open air vendors in Sadrith Mora. She is on the East side of the tower in the middle of town. Simply take a guild guide to the Sadrith Mora mages' hall, and then leave the imperial fort and take the right fork in the road when you get to the Telvanni part of town. The Vendor is a female redguard if I remember correctly.

There are several places to find it. as allwhites said, u may obtain it from the blacksmith but later in the game since enemies 'size up' to you i have encountered many hlaalu guards wielding this weapon due to the fact its the same material as their armour

Even though most people don't like to cheat i just do this.

Open the console(with this key~)and type TGM EXACTLY like that to enable god mode. Then type this EXACTLY as I have it. COC "Character Stuff Wonderland". Next you will have to kill a bunch of monsters(some are immune to normal weapons).Finally you can look inside the chest that says Large Chest of Weapons, and THE FIRST ONE should(hence the word SHOULD)be the bonemold longbow.

Try looking around the gaurd houses of ald-ruhn