I sell rigging for use on buildings, Ballustrades & the like. To be honest with you, for the type of gear you need, just go to your local supplier, there's propably one at your Marina, the difference from one supplier to another is insignificant.
In Southampton, Hamble Ropes and Rigging in Oxford Street. We use them for stuff at work as well, but they don't give discount. Or try Bursledon Riggers out beside Alladin's cave. I think there's one at Shamrock Quay (William Street) as well.
Just a thought - How close are you to replacing the standing rigging? If that job's coming up (terrified quivering from wallet...!) you may be able to recycle the old shrouds, etc.