Hi, battery came from SCA race & rally in Norwich (local to me) but if you google odyssey race battreys you will find plenty as lots of places now stock them over the varly battreys due to more availability, there not cheap though expect to pay £90+ just for the bat.
As for cable I got it from a cable wholesalers, paid £19 for around 30m, so much cheaper than any auto supplies ask any sparky round you way and they should be able to tell you the location of the nearest wholesalers.
As for terminals and silicone sleeves they came from my boyfriend works
maintenance department

but any cable wholesaler should stock these also and they will beable to recommend the correct fit and type.
If you don't mind paying a little extra places like Merlin motorsport, rally design and Demon Tweeks will stock everything you need including the battery.