You are right. FM18W08 is the only option available in the wide voltage range. Both SG and SGTR are same. SGTR says you will get them in a Tape & Reel package.
We do not have a real time clock option with your specifications. But we do have in either 3V or 5V option and 48-pin package.
If you are considering serial memory for new design, then we have some more RTC options in both serial (SPI/I2C) F-RAM and nvSRAM devices.