Following this documentation: https://zypp.postgresql.org/howtozypp.php
Ran the following commands:
zypper addrepo https://download.postgresql.org/pub/...g-sles-10.repo
zypper refresh
zypper install SUSEConnect
SUSEConnect -p PackageHub/12.3/x86_64
SUSEConnect -p sle-sdk/12.3/x86_64
zypper install postgresql10-server

Just rebuilt the server again this time with SLES12sp3. Ran through the same steps and still no pgcrypto.control file in /usr/share/postgresql10/extensions