You should have received a sensor unit when you purchased the keyboard. Unless you have this I'm afraid the keyboard is useless. The keyboard I'm using to type this is a wireless type but the sensor is built into the actual computer so the keyboard is of no use to anyone unless they have the same type computer. I've never seen a sensor on it's own without the keyboard at auctions but I've seen plenty of keyboards without sensors.
The sensor can be in many forms but usually it's a half round module with a flat face which points toward the keyboard and has a cable attached with a USB plug on the end.
I'd be returning to where you got the keyboard and asking for the module. If it's not available, ask for a refund as it's of no use as it is. Maybe the seller didn't realise the module actually went with the keyboard and still has it. It's worth a try.
If you do get hold of the module write back and I will then try to track down the driver although your computer may recognize the sensor and have the driver ready to go. Often just plugging it in Windows will recognize it and load it all for you. A user guide isn't really necessary as it's just a matter of plugging in your sensor loading or let windows load the driver, pop a battery or two (usually AAA type) in the keyboard, pressing the one and only button on the bottom of the keyboard to sync the keyboard to the remote and away you go. All you have to do is replace the batteries when prompted or the keyboard becomes erratic or stops working. BUT try to get that module first or your money back.

As a last resort you could possibly try the manufacturers or importers for a spare module.

Good Luck