Hello! There are a few different ways to obtain Moonstones. They're the premium currency of Lorwolf, so the first & quickest way to get them is to purchase them outright from the Premium Shop. There are, however, other options for getting them. I've outlined these below!
If you like grinding pebbles, then people do like to sell MS on the Flea Market. The value of Moonstones can range anywhere from around 14kp-15kp to 19kp-20kp. Right now, it looks like they're selling at a rate of 1 MS to 18,999kp. It often changes based on the day! You can also sell wolves/items for Moonstones; G2 Bracchus, Zerda, & Volmyr generally go for quite a bit, but WWs are another good way to get Moonstones. Try searching around on the Flea Market and seeing what people are selling for Moonstones; it might help you price some things for yourself!
You can also earn something called Moonstone Shards, which can be crafted into Moonstones at a rate of 10 Moonstone Shards to 1 MS (you'll also need 5 Bone Paste to craft them). Moonstone Shards can be earned through a number of ways. Doing activities like cooking, mining, & fishing can net you Moonstone Shards, and participating in the Gauntlet can also award you with Moonstone Shards. You can earn up to 25 Moonstone Shards daily this way if I remember correctly! Someone else can correct me if I'm wrong on that number.
In addition to regular activities, you'll also notice on your Daily Activities bar at the top of the screen that some completed dailies will earn you Moonstone Shards in addition to your typical tickets & pebbles. You can earn up to 3 Moonstone Shards daily this way, I believe.
Another very easy way to get Moonstone Shards is to participate in the Pageant! If you vote each day, you earn more Moonstone Shards there as well.
Again, these shards can be crafted into Moonstones, so they're not a bad thing to farm. :)
Hope this helps!