Long long repair time on contract purchase car

[WahooBuckeroo]

I had a RTA 6 weeks ago and the car was taken to an approved Mercedes Dealer for repair as per MB Finance request. The car in question is a Mercedes R350 and they are telling me it "may" be repaired in 6-8 weeks due to lack of bonnet anywhere in Europe (they have mentioned getting a batch made). Allowing for summer factory shut downs etc and an element of trying to keep me happy Iwould think this would be more like September-ish when the repair is completed. The car is financed through a contract purchase scheme and ends 25th March 2017. I have a Toyota Aygo courtesy car which isn't exactly a suitable replacement for an R Class so for the summer I would have to hire a replacement in at circa £2K+ to meet the family needs.
I don't think this is acceptabe for MB to sell a car and then not have spares in stock (I could understand if I was running something exotic). I have threatened to cancel the direct debit but just wondered if anyone else had had this problem?