Kebrells in Coventry will have all the bolts you need. They were in Harper Road just off London Road at the town end but they may have moved up to Canley. Probably best to take the old bolts (or what's left of them) down there
https://www.google.com/maps/place/Kebrell+Nuts+%26+Bolts+Ltd/@52.398684,-1.555828,15z/data=!4m5!3m4!1s0x0:0x3d6c75b8baf3a93e!8m2!3d52.398684!4d-1.555828