Just lvl up a bit and get the Wyrmslayer! That's one of the best bows and it is possible to get it on low lvl (I got my at about lvl 10).
Its not easy, but with a rogue it's possible. You need speed potions, evasion and a big emerald. Get to Maze of lamph lvl 2 and to the priest to rest. Don't fight, just run using speed potions and evasion all the time. Get to the poison dragon, use your companion as meat shield, grub the bow and get the hell out of there