Currently there is no Rebol 3 PostgresSQL driver. The Rebol 2 driver is quite concise so migrating it to Rebol 3 might be an option. If you are interested in updating the Rebol 2 one then you will find this tutorial by Graham Chiu very useful:
https://github.com/gchiu/rebol.net/blob/master/docs/Writing_a_Network_Scheme.adoc
@rebolek has also written a Redis protocol which may serve as a useful reference:
https://github.com/rebolek/prot-redis
To the best of my knowledge the most recent Rebol 2 version is here:
http://softinnov.org/rebol/pgsql.shtml
The author of the Rebol 2 PostgresSQL driver is still active in the community (and is now developing the Red language) so he may be able to help with support and suggestions. Come and visit us over in the Stack Overflow Rebol and Red chat room and hopefully we can offer further help.