At work, so I'm not able to check references easily, but I know Jim Steinmeyer has published/marketed some jumbo card 3-Card Monte routines. Soft-Shoe Monte is marketed by him, and I know his lecture notes Artificial Conclusions covers a jumbo version. I think there's also one in Device & Illusion.
In the Vernon Chronicles, Volume 3, the explanation for his Joker Monte might have some possibilities for your needs.
Would a version of the Martin Lewis Sidewalk Shuffle be a possibility?
Or, perhaps something with the Takagi Miracle Monte gimmicked card (described in The Amazing Miracles of Shigeo Takagi).
And there's also the marketed routine by Meir Yedid, Jumbo Quick Monte.
Hope this helps!