UK source of small UNC nuts and bolts?

This is classiccmp-related in that I am repairing an old HP 'Multiprogrammer' (a modular input/output system for HP2100s, HPIB machines, etc). While dismantling it I had one screw shear off and had to drill out pop-rivets holding a heatsink to the side casting. So waht I am looking for is a source of small UNC nuts and bolts in reasonable quantites. 'Small' means 4-40, 6-32 and 8-32. I would be looking for countersunk and pan head scewws, nuts, lockwashers, etc. 'Reasonable quantities' would be a bag of 100. These are not at all common in the UK, we tend to use BA (older machines) or metric (M3/M4 sizes). Does anyone know a company who can sypply these to the UK? Preferably one based in the UK (to save on postage charges), but there's no real problem with shipping a ag of nuts and bolts from anywhere. -tony