lunchbox scamatic

You mean the bottle cap mine, but you can find a schematic for it at the green pastures disposal site but you need a radiation suti to get to it.

There are three of these in the game. Having one schematic allows you to construct one using the required parts, having two allows you to construct two mines for the price of one, and having all three allows you to construct three for the price of one. Here are there locations:

1 - Complete the optional objective in the Landmine section of the quest, "The Wasteland Survival Guide" by disarming a frag mine and returning it to Moira during the 'Minefield' section. Do this by walking up to the landmine and hitting A on it once to disarm, and once more to pick it up. If you blew up Megaton, go to Underworld and Moira will be there as a Ghoul, offering the exact same quest.
2 - There is one somewhere in the Green Pastures Disposal Site. I'm not sure where, but me sure to pack some rad-away. I'm not 100% sure about this one, so make sure to double check. It might be somewhere else, in a gas station or something.
3 - The last one is the hardest to get. It is in the safe in Herbert "Daring" Dashwood's room in Tenpenny Tower. The catch? You can't pick the lock on it, and the key can't be pickpocketed or gotten off of Dashwood's dead body. That means that there's only one way to do this: Talk to Dashwood and ask him abut Argyle. If you've been keeping up with the radio show on GNR, you'll know that Argyle is Dashwood's Ghoul Manservant. Dashwood will tell you that he and Argyle split up shortly after their last adventure, and he'd give anything to know where he is now. That "anything" is his key. Argyle is in Rockopolis, the place from the radio show. This location is not marked on your map and is hard to find. Check the Fallout wiki page for more specific directions, but it's on the west side of the map, I believe it's close to Smith Casey's Garage (The location of Vault 112.) The entrance it hard to spot, as it's simply a boulder with a small string of flags above it. At night, the rock glows, so if possible, that'd be the best time to find it. Once you get inside, you'll realize that there's not much to the place. There's a 10mm pistol, a holotape describing that the Ghouls left to somewhere called "The Pitt" (The Fallout 3 DLC :D). Now, continued on and after a few steps, you'll find Argyle's body. Yup, he's dead. If you want, check to see if he has anything good on his body, grab the Unarmed Bobblehead next to him, and head back to Tenpenny Tower. Once you get there, tell Dashwood that Argyle is dead. He'll be shocked, claiming that he expected Argyle to outlive him by at least a hundred years. He'll then thank you and reward you with the key to his safe. Be careful, as it's still considered theft to take the stuff from his safe, even after he's given you the key. Open it when he's not around, and find some really good stuff in the safe, including the bottlecap mine schematics.

I hope this helps!

In addition to the one you get in Mega you can also get it at Jocko's Pop & Gas Stop, northwest of Tenpenny Tower and east of Girdershade; in Dashwood's safe, in Tenpenny Tower, received for completing A Manhandled Manservant.
One can be bought from Knick Knack in Little Lamplight.

Inside Dashwood's safe in Tenpenny Tower.