While there isn’t any calliope/classic big top music in Syrinscape right now, there are some sounds that can give you a good Midway/festival/carnival feel in the interim. Attack on Sandpoint (from Rise of the Runelords’ Burnt Offerings set) has a town festival with crowd sounds, happily yelling kids, and general town square noise (it also has fires and explosions, which could double for fireworks or fire-based acts). Brindle Town also has a lot of interesting “passers by” for a Midway. Spooky has a lot of crazy laughter for a Hall of Mirrors or a freak show. Some of the music from Desert Camp might be suitable for exotic entertainments from far-off lands. You could throw in some growls and animal sounds from Mountain Pass (which has bears, lizards, and eagles), Jungle (Tropical) (apes and dinosaurs), Dragon Battle (roars), Elven Vale Day or Elven Vale Night (weird wildlife), or Witchwood (also weird wildlife) for exotic beasts being on display or in acts. Wagon Journey has sounds of a wooden caravan, if the circus is coming into down. It also has horses, for equestrian acts.
The soon-to-be released Gnomeland Security has fiery rockets, a chimera, and a lot of silly antics, along with some hoedown music, which could suit for some parts of the circus.
In the meanwhile, there is a group called Nox Arcana and another called Midnight Syndicate that both do themed ambient sounds/music. Nox Arcana have an album called Carnival of Lost Souls and Midnight Syndicate has one called Carnival Arcane, both with creepy carnival sounds and music. While they don’t have the versatility of Syrinscape, they both have some of the carnival-type music (albeit with a creepier bent).