Here in various lengths. Not cheap, but hard to find if you need longer than standard

Google 'DJ Evans' based in Bury St Edmunds.

Great for all sorts of odd sized bolts and well known for being able to source them.

I'm not sure how 1000N/mm^2 is 2-3 times stronger than 800N/mm^2

btw - I found some std. ones the other day, I'll have to check, but I might have a spare set....
watch out for my big garage clearance thread {with optional free delivery to stoneleigh} coming soon