I have these wheels on my 155 too, and i agree, beautiful wheels. A pig to keep clean though! I posted an email adress above of someone who may be able to help you. I'll give it again : email@example.com based in Denmark, but he speaks good english. I lost contact with him some time ago just after i got my wheels(six months), but try him, he said he had the correct locking bolts to fit. You can use the Original Alfa locking bolts, but most people i spoke to didn't reccomend doing this for too long, although i've had no problems in over six months.
I think Henry means the vari bolts, i've not seen locking vari bolts in Halfords.
The reason the Alfa locking bolts are liable to break (under extreme loads)is because they can't sit perfectly in their location in the 100 pcd wheel. This is because they don't have the collar like on the 'vari bolts'.
The collar part sits in the recess in the wheel where the bolt goes, the bolt itself then moves within this collar 1mm to the side to be able to screw into the thread in the wheel hub.
The key is this movable collar, without it the bolt can't move the extra 1mm it needs to, to be able to effectively make the 100 pcd wheel a 98 pcd.
Any heavy shock (as Henry experienced) may cause the Alfa locking bolt to break because of the extra load it is under. Err, i hope this makes sense! Another way to put it would be to imagine two holes of equal size placed over eachover, now move one of these holes to the side by 1mm. This is what the 100 pcd wheel will look like mounted on a 155 hub.The varibolts make up this difference. If you had normal bolts all round, you'd have to stick them in at 45 degree angles!
Sorry if i've repeated myself. Just hope this clears thing up! I'll try Martin at Bigwheels again, see if he remembers me, and let you guys know. After all i need these locking bolts aswell! Jeez, another long post!
Hope this helps.
btw Sentenal, thanks for the tips!