Magic knuckles - future content

Neither of you are correct. The regular Shyllien Knuckles are from just logging in during the release of the event, the Merlin's Shyllien Knuckles are from gachapons.
Some common misconceptions:

• People think Zero/Hero/Elite Hero cards come with clothing and/or weapons like limited edition character cards, they do not.
• Hero clothing are sold separately in a bag that gives a 100% chance of giving you every piece of the set, not a gachapon. And this only includes clothing, not the weapons. Despite Merlin's weapon being knuckles, his set comes with gloves.
• Only craftable hero weapon so far is the Treasure Hunter's L-Rod Guns.
• After the corresponding events are over, no way to get new Shyllien Knuckles. But you can buy a Microphone and a Guard Cylinder from regular NPCs, just not the best/better ones. The weaker Chef's Dual Knife might be sold at NPCs, and as previously said, both guns from Treasure Hunter can be made with engineering (the better of the two requires r2 Engineering and ingredients from both Hillwen and from Woc Dungeon found via r5+ exploration.)

Edit: Also, just because KR got them from one method doesn't mean we will get them from the same method, for all we know there may not be any free login knuckles here.