The Snugride car seats are, unfortunately, only compatible with Graco double pushchairs, so you limit yourself to the cheaper Graco double buggies which, I'm afraid, are not the best in terms of pushing as their wheels are really hard and simple. A large, heavy toddler will make the ride quite difficult in any of them, I am sorry to say. Apart from this one, I would actually not recommend any of the Graco double buggies as the tandem models are very, VERY hard to operate. And about if and when Graco will issue this model, or a similar model again, I have no news, they say nothing on the subject at the moment.
Sorry for the bad news. If you'd be willing not to use the Graco car seat, I would most definitely suggest the Valco Snap Duo which had actually a rather long (even if narrow-ish, like all side-by-sides) seats and pushes quite nicely. I did fit a 4 years old in that seat so I was quite pleasantly surprised. A very nice to push and quality (but also expensive) option would be the Baby Jogger City Mini Double2/Baby Jogger City Mini GT2 Double.
Another option for you, if you are going to keep and want to use the Snugride capsule for sure, would be the Mountain Buggy Nano Duo which accepts most car seats without adapters needed
(if you only use one car seat at a time) as it straps the car seat onto the seat with a strap belt.