What are the bets ways to obtain them so I can upgrade my weapon?

@Morgothryuzaki what I've seen so far is trade 10* weapons in swap shop for excubes. Them use excubes to buy lamda grinders for shop on second floor.. u need 10 excubes for 1 grinder.

Listed up what I could gather. Maybe there are more.

Practical and repeatable

• Daily ARKS mission. 3 per character each day.
• EX-Cube exchange shop. 10 EX-Cubes for 1 lambda grinder.
• Swap shop exchange. 3 rarity 12 weapons for 1 lambda grinder.
• Fresh finds shop daily item. 900k Meseta for 10 lambda grinders.
• Casino prize exchange. 250 CC for 1 lambda grinder. Max of 20 each week.
• Mission pass rewards. 3 lambda grinders for 4 weeks season?

Practical but one time only

• Many Main ARKS missions. Listing all these up is rather meaningless, I suppose
• Girard's client order "Avian Harbinger of Stormwinds". 3 lambda grinders. Only once per account. Can be done on Harukotan TA.

Ways I feel unpractical, due to being difficult, having a low chance of success or for an outrageous rate of exchage.

• Special rewards of recommended quests sometimes have a lambda grinder.
• Swap shop exchange, 10 eggs (rarity 10 or 11) for 1 lambda grinder.
• Gal Gryphon drop. Note that Harukotan TA doesn't count.
• Elite Training: Heaven & Earth enemy drop. Note that you need to complete 5 stages to get any items back.
• Titles for completing stage orders of Elite Training: Heaven & Earth. There are 4 titles. At the maximum, you can earn 60 lamda grinders by completing 100 stage orders.

Notes: the stage orders titles are guess made from JP server data. There may be other titles not listed here which rewards lambda grinders. Also, I've ignored some ways which are available in JP, but currently not in NA.

I kinda find the ex cubes trade really outrageous personally. But thanks! I'm screnshotting that

@Morgothryuzaki I forgot to mention, but you are compacting the fodders to a 12-star weapon before feeding it to the 13-star weapon, aren't you?

Playing Summoner and doing max level stuff as Summoner. Instead to get Dio weapons and stuff you get eggs, and those can be traded for Lamba in swap shop.

@Fiona-Respha I am what?

@Morgothryuzaki You're trying to keep the number of lambda grinders minimum, say like 5 lambda grinders to make a 13-star weapon from 0 to +30, right?

@Fiona-Respha Oh so that is what you mean. I am waiting to get my Nemesis before I bother with lambas. I used 3 lambdas to get my current to +8 and I won't touch it anymore until then.

There will be many guides on how to enhance +13 weapons effectively. Better guides should have listed some ways to cut the number of lambda grinders needed. Those will be helpful, I suppose

EDIT: 3 for +8 is a bit luxury use of lambdas, I felt.