I think the most readily available is DevNet Sandbox's Meraki Always On. However, it is a read-only environment.
There is also DevNet Sandbox's Meraki Enterprise, which is a bit more flexible, but reservations are required.
Cisco DevNet Sandbox - try out online developer environments - Cisco DevNet
https://developer.cisco.com/site/sandbox/
Cisco dCloud also has several Meraki environments.