Id do B and C, ring around and see if theres anyone else, but regardless of if you find someone or not, Id still say its good to practice with your partner.
I had a similar situation in that my instructor was super unreliable, kept cancelling on me last minute, or cutting lessons short. I only ended up having 4 lessons with him total, the rest of the time I went with my dad. Driving instructors near me have a massive wait list, but i did manage to find a driving instructor to do a mock test with me only, which I thought really helped. When you ring/ email other schools, if they say no, id ask if they can at least do a one off mock test (if you want to do one). Worse case scenario just practice with your partner. I did it with my dad and passed 1st time, even though my dad knows nothing about driving exams (in fact he told me some incorrect information- so if your partner tries to tell you how to do something id definitely take it with a pinch of salt and look up the correct way of doing it later, sorry partner lol). Good luck!