Is it faulty - are you looking to replace it ?
There are places that refurbish locks if it's no longer in production, but this is only cost effective for antique/rare locks where a replacement would be difficult.
It looks like a Gibbons 2 lever - are there are markings on the faceplate ?.
If looking for a replacement, ensure you correctly measure the backset (distance from edge of door to centre of keyhole), Spindle centre (distance from edge of door to centre of spindle hole), and your facelate length/width to minimise the amount of repair to the door.
If it's off a final exit door, then you should be looking to replace it with a BS rated lock, otherwise your insurance cover is likely to be invalidated should you be broken-into via this door.