Attempting to upgrade VMware tools on vSRX 3.0 ends with error "The required VMware Tools ISO image does not exist or is inaccessible. vix error code = 21000 No VMware Tools package is available".

• VMware Tools upgrade fails on vSRX 3.0.
• One of these errors is showing:

vSRX 3.0 architecture is based on FreeBSD 11 and not Linux hence upgrade instructions con KB31495 [juniper.net] do not apply to this unit. The VMware tools (binaries and libraries) are packaged into the vSRX Virtual Firewall image file and allow VM instances to query information from hypervisor and then set or use such information. by the VM instance itself.

You can confirm the vSRX differences between 2.0 and 3.0 below:

https://www.juniper.net/documentation/en_US/vsrx/information-products/topic-collections/release-notes/18.4/topic-98044.html#jd0e167

Also, as the below document explains, the VMware tools are included (packaged) in the image. 

https://www.juniper.net/documentation/us/en/software/vsrx/vsrx-consolidated-deployment-guide/vsrx-consolidated-deployment-guides/topics/topic-map/security-vsrx-vmware-tools-support.html