You can deploy a FortiGate-VM (BYOL) outside the marketplace product listing using a custom ARM template in the Azure portal. This is an alternative method for if you want to deploy FortiGate-VM on instance types/sizes that you cannot find on the FortiGate-VM marketplace launcher. Some instance types of your choice may not properly boot up or run due to lack of official FortiGate-VM instance support.
There is a bare minimum set of templates available for your deployment.
You can also specify bootstrapping FortiGate CLI commands within the template and run them at the time of initial bootup.