.

Then, how did Sirius get a wand?

Sirius most likely stole a wand after escaping from Azkaban. Hagrid's wand was broken when he was expelled. The Death Eaters returning to Voldemort kidnapped Ollivander and presumably forced him to make new wands for Bellatrix Lestrange and her companions after they escaped from Azkaban.

Furthermore, what was Voldemort's wand made out of? yew

Also know, how did Voldemort find out about the elder wand?

Voldemort broke into the prison Nurmengard Castle, where Gellert Grindelwald was being held, and demanded to know the location of the Elder Wand. It was only during the confrontation in Grindelwald's cell that Voldemort learned Albus Dumbledore had claimed the wand in a duel decades back.

Who has Voldemort's wand?

Tom Riddle's wand was 13½" long, crafted from yew, and affixed with a phoenix feather core, and it belonged to Tom Riddle, the wizard who later became known as Lord Voldemort.