We do not have a direct replacement for this antenna unless you are looking to change your device to incorporation a surface mounted antenna that would solder onto a PCB like our A10340H or the SR4L034. You could also use one of our external terminal antennas like the SREL036. All of these antennas cover the frequency bands you are interested in and if you order the SMD antennas on their evaluation boards they will come with an SMA connector. The external antenna comes with an SMA connector as it is.
Other than that, Digikey and Micro-semiconductor.com have some stock of the B5812 left.