Well, Semtech's reference implementation supports class C devices, and IBM's LoRaWAN in C partially supports class B devices.
While Microchip's RN2483 only supports class A devices, there are plenty of modules available that give direct SPI access to the SX1272/SX1276 chip allowing you to run these stacks (or you can just build your own hardware).
As for the server; the loriot.io network server seems to support class C devices, however I have only tested class A devices on that platform.