Recent vintage chrony man pages say:
sourcedir directory...
The sourcedir directive is identical to the confdir directive, except the configuration
files have the .sources suffix, they can only specify NTP sources (i.e. the server, pool,
and peer directives), they are expected to have all lines terminated by the newline
character, and they can be reloaded by the reload sources command in chronyc. It is
particularly useful with dynamic sources like NTP servers received from a DHCP server,
which can be written to a file specific to the network interface by a networking script.
This directive can be used multiple times.
An example of the directive is:
sourcedir /var/run/chrony-dhcp
Admittedly this is more of a hint than a recipe.