Yup, bought a set yesterday, B&Q of all places, only ones I've found, SF don't even seem to do them -
http://www.diy.com/departments/coupling-bolt-set-l-440mm-dia-70mm-set-of-1/1484896_BQ.prd
http://www.diy.com/departments/coupling-bolt-set-l-440mm-dia-70mm-set-of-1/1484896_BQ.prd