The reason you can't find them is they are not called security bolts. That term refers to the type of head.
The correct name for them is Cabinet Bolt set. Never heard of Sex bolt (although google does find a load), the link above also calls them Barrel nuts, they are something totally different.
A common use for M6 and down is Kitchen cabinets and the ones with Security heads are used in the cubical's of public toilets. While over M6 are used in the construction of Wagon backs etc.
I have considered this but I'm manufacturing things for resale so the less fecking about I can do the better, and it may not be a lot but it all adds up. If I can find the right item at the right price I'd rather just have it sitting on the shelf ready to use, with all it's protective coating in place.