I would use an RTC chip (my favorite is the pcf8563t - 200nA operation) as, afaik, all have a programmable square wave available at the clock out pin. The default output (open drain, enabled at power on) is 32kHz and you may set it to ie. 1024 Hz, 32 Hz, and 1 Hz at least with above chip. The chip is fine-tuned for 32khz crystals, and, as a bonus, you'll get an RTC as well :).