Here are some suggestions that should be helpful.
Hawk Cars in the U.K. is one of the "go to" places for AC Mk IV parts. I have some on order now for my 1987 Mk IV. Gerry Hawkridge is the owner and a great guy. The web site is
Hawk Cars - manufacturers of the 289, 427 and HF Series. I understand that they have body shells and Gerry is a Mk IV owner.
Here are a couple of others. The AC Heritage web site and Brooklands Motor Company web site are below. AC Heritage and Brooklands may be related and I believe are also a good parts source and may have aluminum body panels. I am not totally enlightened on their relationship with the original AC Cars Ltd., but may be licensed to use the logo and provide parts.
accars.co.uk
Brooklands Motor Company Front Page
As you own a Mk IV, I strongly suggest that you join the AC Owners Club. There is a wealth of information in the forums on the web site, and there is one forum devoted to the Mk IV. The cost to join is reasonable, and you get a club magazine every month that is interesting and there are good resources in the magazine and from fellow AC owners on the MK IV forum.
http://www.acownersclub.co.uk/
Sorry you got in an accident....I hope the above helps