Got mine from Radio Shack. They had just about any size you can think of.
I tried the 7.5 in my 82 cm450. It worked in the headlight circuit, but not in the taillight. Weird. Went around to all the local auto places and a Honda dealer and couldn't find the 7. Then one of the guys at Auto Zone, told me to check out Radio Shack. Sure enough, they had it. Around $2 for a pack.