I will assume you are wanting to purchase from here.
If you have trouble getting them here, you can search for train set or pinball and find those qualities.
LED's, may be an option unless you want original incandescent.
Automobile 12V LED will work... if you get the right ones. Be carefull though most have the + on one side and - on the other, it matters. Slot bulbs can be inserted either way because the bulb leads are diagonal if you understand what I am trying to say.
+ + + -
@ @
- - + - I am pretty sure this is correct 'picture'
Tony