The only ways to find a higher quality of one (instead of primitive) on mobile is to:

(listed from most conventional to least conventional)

1. Go to a dungeon with the blueprint as one of its "featured loot", open the specific featured loot dungeon chest that may not be distinguishable from other dungeon chests, get the blueprint, beat the dungeon, and craft it

-There is usually 3 other items in the "featured loot" chest, it may not be a straight 1 in 4 chance to get it.

-It is not guaranteed for lower difficulties to get the ascendant blueprints

-On singleplayer, you can save your game right before you touch the featured loot chest and open it, if it isn't the item you want, refresh and try again.

2. Buy an extravagant gift on multiplayer for 60 amber and mail it to somebody

-There is a 2/27 chance to get either a mastercraft or ascendant fabricated sniper rifle blueprint

-Another person can also buy an extravagant gift and mail it to your mailbox, and you can open the mailbox to recieve the gift.

2. Collect them from holiday loot drops which spawn at night (e.g. thanksgiving cornucopias, christmas presents, halloween pumpkins)

-They may not be doing these events anymore, or ever.

3. Fishing

-There is a 3% chance to fish up blueprints if you catch a fish, but it increases the higher the fish size

-There is a 1 in 16 chance of getting a fabricated sniper rifle blueprint out of other items

4. Open the red loot crate in the snow cave

-You have to be level 55 to open one

-It is located in the 3rd section of the cave with the ice cliffs

-It is a 1 in 38 chance to get either the item or the blueprint

This sniper rifle can shoot multiple bullets without reloading with big damage which makes it really op