VCTCXO control voltage circuit recommendations?
If you already have a good TCXO, why not do the last step, and sync it with GPS?

With a simple controller you can measure the number of TXCO cycles per 1pps pulse of a simple GPS receiver, and use the processor's PWM output to feed the control input. After a long period of operation, you could then store the PWM value in internal EEPROM, if you need/want to disconnect the GPS receiver. You could even maintain ageing characteristics.

A small PIC controller can have 10bit resolution in the PWM!