Surepet RFID collar tag (Kingston Hill KT2)

My cat lost his collar today so I’m desperately searching for a replacement RFID for his Surepet cat flap, which seem to be out of stock everywhere local. He’s chipped but it’s unreliable - we’re getting it checked at our next vet visit in July - so this is just to tide him over and make sure he doesn’t get stuck outside, bless him! If anyone can help us out we’d be really grateful. Picture as cat tax