Yeah i know your pain. it is honestly a really hard gun to get in other maps. You honestly just have to get lucky. It might help if you have the mystery box upgrade/ permaperk that allows you to get better weapons.
Just to point out a few things about getting MK2 on other maps.
1. Box on Origins is a Beatch, prepare to spend about 100k before you will see it, most likely same for other maps.
2.Only ONE player in a team can get this gun unless you play Buried.
3.You can not carry 2 ray guns... so if you have Ray you have to drop it to fish for MK2.
lol guys you might not believe me, but I do get MKII and I trade it with other weapon from the box and YOU can get raygun mark I and II same time...and last but not the last I got it like 6 times from the same game...I trade it cuz need ammo
dont know if this will help you.. or even if I'm 100% correct. However, I have notice that while playing MOTD ( fav map ) I always build up points then hit the box as many times as I can to get what ever weapon tickles my fancy to take to the bridge to P.A.P. I always shoot for the AK47.. never get it. I've gotten the Ray gun & Blundergat..all the f*%kin time. Anyway..try this. Basicly , get into trouble. I notice that while running a train, and not having a very powerful gun on higher rounds , I always make good on the box. ALWAYS. like lets say I'm on round 21.. I got the Uzi PAP'd..and maybe B23R as well. lets say I got about 20-25 Z's in my train. if I hit the box..W.Weapon or Ray Ray for sure.. every single time. I'm sure I've gotten the Mark 2 on MOTD before.. but I dont care for it, so I would have traded it. Try it.. could'nt hurt. Oh also try it when your low on ammo..
If you pray hard enough maybe....just maybe you'll get it.
I've only gotten the RGM2 a couple of times on tranzit and like a previous posters said I didn't get it till after I had a hundred thousand points and a teddy bear was on the box. but I do get it all the time on Buried. Found a nice little cheat on how to get the RGM2 every time out of the box on buried on YouTube.
It involves downing yourself 5 times after buying all 4 perks every time you go down, right?