Questing in Suramar I have found that the Jandvik Ripfangs, only source of the "Rustic" wolf look, become non-attackable after you reach a certain point in the quest chain. Essentially, the quest NPC tells the villagers you're under her protection and everything becomes neutral / passive. Maybe there's a later twist where they all become aggressive again, but the chain is bugged and I can't progress any further, but such a twist seems doubtful. Also, they don't have a faction, so you can't put yourself "at war" with them.
So unless they add it to another wolf it will also become unavailable after you do that quest.

Maybe there's a rare somewhere, but if so I'm not yet aware of it. And the yellow rustic version was never available (again, to my knowledge, which is limited) anyway.
What I'm going to do is:
- post on the forum here a definitive list of Legion model colours that we can't find on tameable mobs. I already have such a list so it's easy.
- see if anyone knows of sources of any that simply may not have been reported yet. Colours used on very rare (or well-hidden) mobs are easy to miss.
- post a request on the official Legion forums for switching colours of certain mobs to allow some of the colours that are currently unavailable and hope for support from other Petopians. They may still ignore it but we can only try

I see it as the only recourse at this stage.