The library workflows for clone/customize indeed are missing support for that nic type due to that action not being updated. Here's what you can do as a work-around:
- Duplicate the library workflow if you haven't already and give it your own name (ie: Custom Clone and Customize Linux)
- Edit the workflow and remove that call to the getNicByNumber action
- Add a Scriptable task to the workflow in the place that the getNicByNumber action was in
- Paste the following code into that Scriptable task:
var devices = vm.config.hardware.device;
var sourceVirtualEthernetCard = null;
if (nicPosition <= 0 || nicPosition > 5) nicPosition = 1;
var actualPos = 1;
for (var i in devices) {
if (devices[i] instanceof VcVirtualE1000 || devices[i] instanceof VcVirtualVmxnet || devices[i] instanceof VcVirtualPCNet32 || devices[i] instanceof VcVirtualVmxnet2 || devices[i] instanceof VcVirtualVmxnet3) {
if (actualPos++ == nicPosition) {
System.log("Found a Virtual Ethernet card at " + i + ". Key: " + devices[i].key);
sourceVirtualEthernetCard = devices[i];
}
}
}
- Add two inputs to that scriptable task:
- vm (VC:VirtualMachine) - bind to the "vm" input parameter
- nicPosition (number) - bind to the "nicPosition" attribute
- Add one output to that task:
- sourceVirtualEthernetCard (any) - bind to the "sourceVirtualEthernetCard" attribute
- Click the "Validate" button at the top of the screen, make sure you don't have any errors
- Save and Close
- Test, Test, and Test again
I have had to do this in a number of the projects I have worked on as well. The code snippet above is nearly identical to that of the action... I simply added a check for the VMXnet3 type 
