I saw a post from about a year ago saying that there was never a script developed to check if a user has specific souvenirs because reviewers don't allow this. However, in the past year something has changed with souvenirs.
There are now specific souvenirs that are not time-limited and not based on a country.
I'm talking about the 'Celebrating 25 years' souvenir that everyone gets when they complete the coorsponding treasure collection, as well as the newer 'Making Memories: Crafty Cacher' souvenir. It seems like the trend will continue to release more permanent souvenirs that are awarded when specific treasure collections are completed.
I understand why reviewers have never allowed challenges based on specific souvenirs. Prior to this year the only permanent souvenirs were countries, it doesn't really make sense to have a challenge for these since it's just overcomplicating things. 'Find 1 cache in Canada' vs. 'Obtain the Canada souvenir'.
I do think there would be a valid reason to have specific souvenirs in challenges now though. The two challenges I have created myself are based on the criteria to unlock different treasure collections.
I personally think it would be fun to have a 'Crafty Cacher Challenge' with the requirement being the user has the Crafty Cacher Souvenir. It would be fun to celebrate getting a specific souvenir by being able to log a related challenge cache. As more of this type of souvenir is released, challenges could even be created that require multiple specific souvenirs.
I'm not sure if it will ever happen or be allowed but just wanted to share it's something I would appreciate :)