I don’t have any information about Spike’s status, but this person has another method for resetting the G5 or G6 transmitter clock for iOS users. It looks very cumbersome and you need an Apple computer, but based on the comments it appears to work.
I don’t have need to reset a transmitter at this point because I thankfully did it with Spike before it disappeared. But if it isn’t available when I have to reset again, I’ll give this a shot.