The mount from the other Classic bundle is sold on the modern game store (viridian phase-hunter) and the Kalu’ak whalebone glider is also available on the Classic store, so it seems like the Tuskarr shoreglider should’ve been added to the store by now for modern WoW. Please Blizzard 
Hello there Mairi,
While I understand past mounts in this situation made it to the shop as standalone purchases, that isn’t a guarantee it will be the case for all such mounts.
It may of course still happen in the future, or become obtainable some other way, though I’m afraid it isn’t something Customer Support gets to decide – as always, be sure to share your suggestions and feedback in the appropriate forum section.
I hope you’ll be able to add it to your collection somehow soon!