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..
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?