Delco AM push button radio bulbs???

[wlsn_jss]

I sure hope I posted this in the correct forum/thread. . .
I'm a purist when it comes to the original appearance of my C/10's. . . inside and out. That being said, I am content with the sound and look of the original AM push button radio (with a little help from an FM converter). My radio is the original Delco GM 7305841 from my '71 GMC.
My radio works great, however, I thought that the lamp bulb was simply blown which illuminates the AM dial.
However, when I pulled the radio and disassembled it, the bulb was missing completely.
Does anyone know the stock/part number of this bulb? If I know the part number I feel sure I can grab one at my local parts store or at Radio Shack.
Thank you for any assistance anyone can offer me on this one.