Hi there @surnita
Unfortunately giffgaff dont send out notifications for new devices available and we are giffgaff members just like yourself,so we dont know when new stock arrives unfortunately.
If your planning to buy any device from giffgaff, and it's showing as out of stock, as soon as a member adds their new device to there basket, it reserves the device for 30 minutes , and not all of those members will complete their purchase to the end,so you've got to be quick.
After the 30 minutes reservation period is up, the device will become available again,so I would personally just keep checking back and look for stock that has been made available again.
Please also click onto this link http://giffgaff.com/phones
For more info regarding buying a phone from giffgaff, click here http://community.giffgaff.com/t5/Tips-Advice/Buying-a-giffgaff-phone/td-p/10608547
I've also found you this link http://community.giffgaff.com/t5/Getting-started/Buying-a-giffgaff-phone-with-a-loan/ta-p/10724769