"........Every time this comes up people are always recommending getting stuff from Daniel Stern Lighting, and he's got H4 bulbs and relay kits so while I don't personally have his Cibie H4 bulbs (yet) I'll go ahead and put the link here. Daniel Stern Lighting Consultancy and Supply
Thanks for mentioning my go-to guy for all lighting questions.
A small point, the Cibie's are lenses, not bulbs. The bulbs are separate, i.e. Not a "sealed beam" like the original equipment. The Cibie lens have a very pleasing convex curvature, unlike many of the other lenses that come with H-4 conversion kits. My first H-4 was purchased from a well known Mustang vendor, and the headlight lens was as flat as a pancake. Very unappealing on a vintage car, especially a Mustang. Despite the improved light, the flat lens put me off of the H-4 conversion until I happened upon Stern's website and discovered the wonderful Cibie lenses.