While there are plenty of knock-offs of the Nikon MC-36 intervalometer out there, they are all wired, like the original. Yongnuo have made a wireless 2.4GHz version called the Yongnuo MC-36R. The device allows you to remotely trip your camera’s shutter with intervals, self-timer delays or exposure times of up to 100 hours.
There are versions for every major brand of camera and they are available on eBay for around £45.
UPDATE: Pixel have a similar (but different) product out, the TW-282, which has both wired and wireless function. Find it on eBay for a similar price here.