I'm not sure that you chasing around trying to find alternative provision off your own bat will get the outcome you're hoping for. As previous posters have outlined, there are procedures in place when children are excluded from school- this isn't something you can single-handedly solve for your daughter.
Tough as it is (and it sounds utterly soul-destroying, on top of all of your other responsibilities), your husband and daughter have both chosen for him to be the resident parent at this time. It looks like it's time for the two of them to figure out the next steps by dealing with the relevant authorities themselves. Your daughter clearly has very challenging needs, and you have done all you can to support her (along with the school, by the sounds of things). But at the moment, that isn't working for any of you. It's unrealistic to expect anything to change when everyone continues to behave in the same way.
You say that your daughter and Ex expect that she'll be able to pick and choose their favourite from a range of schooling options. It also sounds like they expect you to do the donkey work in terms of sorting all of that out for them. But if you're the only parent in all the meetings , they're going to blame you when you can't conjure up the impossible. That's likely to mean another step down the road of neither of them facing the consequences of their actions (Ex for his abusive behaviour and poor parenting, and DD for her behaviour choices), and a further delay in DD making choices which will help her turn things around.
You can still be there when your daughter needs you, and deep down she seems to understand that your love is unconditional. But to make a change, and for the sake of your health and the other vulnerable people who rely on you, it looks like you need to let your Ex have the responsibilities he demanded.