Hi,
Unfortunately replacing a keyboard is the preferred option, as trying to repair one usually results in more problems than it fixes.
Here is a link to the service manual for a Lenovo G580. It gives detailed steps on how to remove the keyboard.
https://download.lenovo.com/consumer/mobiles_pub/lenovo_g480_g485_g580_g585_g780_hmm_v1.0_english.pdf
On p.110 of the manual you can find the Lenovo part number for your particular keyboard. If you 'Google' ''Lenovo + the appropriate part number'', you will get supplier information.
Hopefully this is of some help.