Not sure why you're looking for agencies for this but my take on building product tours is that it doesn't really require any particular kind of expertise, per se. The only two things needed are,
1. An unrivalled understanding of your product and customers, which only the internal employees will have.
2. Good copywriting skills.
Appcues and Userflow are good alternatives for this. There are many platforms that can help you with many different formats for building product tours though.
Happy to answer any other questions on this!!