In the US, the surplus equipment market occasionally had GPS-trained oscillators that could provide 10Mhz and 1pps clocking as well as NMEA output. They were parts of CDMA cellphone base stations, each of which had at least two. The one I have was made by HP. I also have one that is a Motorola device that was used to synchronize simulcast transmitters in repeaters.
That is the kind of box (from other manufacturers) that we use as well, attached to a PC with 1PPS and NMEA and to the repeater with 10 MHz. Chrony on the PC keeps the Linux clock within 10us (usually within 1-2us) which we require for the simulcast, and 10 MHz provides the exact transmit frequency reference.
Power... well, maybe it has an oven stabilized crystal oscillator. Or very old digital logic that is a bit too power-hungry. Of course a lowcost uBlox/ SiRF module is easy to get going and provide 1PPS for ntpd.
The LeoNTP box is a plugin-and-forget network clock, of course not the cheapest solution. A Raspberry Pi can be used, I have one in the IPv6 NTP pool at 2a00:f10:103:201:ba27:ebff:fefd:984
Rob