For those on Facebook, I recommend the group "Chapala Health Talk." It has been an excellent resource for current info. They have been posting daily updates about vaccine availability (or lack thereof), government announcements/statistics, and daily status on the state of cases lakeside.
For those not on Facebook, I'm sure as soon as there's something official, someone will post it here. But all indications now are there is no info on the when or the where for a second shot. Except to say that when it is offered, it is reported that it will only be for those who have received the first shot. Those who missed the first shot will not be included in this round.