They are available but it is on a case by case basis. The show was done at North Shore Music Theatre in Massachussetts but they paid big money for it (250k is the rumor) and I think that there was a cut of the door given to MTI. NMT is also rumored to get Les Mis for next summer, this is the full version not the School version that has been out there. Again this is going to be prohibitively expensive for small theatres
I think that NMT was an advantageous venue for the rights house because the theatre is in the round so it presents a design challenge. This makes it easy for the rights houses to advertise the show as being able to be done in many different types of venues, and therefore it will be more lucrative for them.
Other than that, did you enjoy the play Mrs Lincoln?