A steel guitar string makes a good tip cleaner. Wrap it around your lamp, behind the reflector, with one end sticking out a bit to keep it easy to find.
A striker assembly is the whole striker gizmo -- spring, cap, wheel, flint holder. Can't remember if also contains a flint. It is rare that it needs to replace it unless the lamp is very old and the striker is frozen. Spare flints are what you need to carry with you, and those are standard lighter flints, available at a drug store. Pack them so they'll stay dry when you're caving.
You can get a wing nut at a hardware store. If the wings don't angle properly to fit, they can be filed -- ask the friendly guys in the shop to do this for you!
Carry a spare!
A ribbed, "stay cool" gasket that goes around the carbide chamber is a good idea. This will keep you from burning your hand when changing carbide, and makes it easy to unscrew the base.
The rubber ring protector ("bumper grip"?) that goes on the seam around the base of the carbide chamber is a good idea as well, for this protects that seam when you bang the bottom on something solid to loosen the spent carbide.
(I'm pretty sure at least IMO carries these last two accessories, and B&B may as well.)
Enjoy!
Cheryl