I can not and don't want to go into the reasoning behind it.
Anyone know what decent shake i can get my hands on?
Make your own. oats, whey, banana, berries in milk, for example.
The problem i have with offering you too much guidance is that you seem to have issues that will affect your progress that you do not want to speak about.
Its kinda hard to offer any advice when we don't know what we are dealing with.
All we can do is offer generic advice, which you seem to not want to take. Cant do much more than that really

If you must buy something from a tub, then find one of the bulk sites as it will be cheaper.
I'll recommend BSD as i buy their other stuff, but have no experience with any mass gainer.