I think the most practical approach is to just get an LED light. The emission pattern of an LED is nothing like the emission pattern of an incandescent filament, so even if you could find an LED replacement, the resulting beam pattern would be all wrong.

For a cost-effective LED headlight, how about the Lyt N: http://harriscyclery.net/product/bus...light-3200.htm

For a taillight, how about... *drum roll* ...a Planet Bike SuperFlash. Or if you really want a generator-powered one, this one's cool: http://harriscyclery.net/product/bus...light-3133.htm