I have Fallout Shelter on two devices- PC and phone. At some point on both of these devices I received a free kind of Lunchbox which gave me one pet. This was before I got 13 people in my Vault. No matter how many game files I start, I have only ever received one on each device. How does this work? What are my chances, if any, of getting a second?
The Fallout Shelter save games are not particularly robust against editing. It is actually JSON formatted.
You can also just edit in more Pet Carriers using Fallout Shelter Save Editor
The only ways to get the pet carriers are limited.
You get one(as mentioned in the question) from a lunchbox
Missions, it is possible to get lunchboxes, Mr. Handies, and, yes, Pet Carriers
And, of course, buying the pet carries