Hideous you say....that is the same dome light as in my '86 Nissan. I was at the TrueValue and the floor guy pointed me to the RV section (Yes, there are still places where they meet you at the door and ask to help you, not like HD, Lowes and etc where you have to beg for help).
The bulb in that thing is nothing special. It is a standard bulb. Autozone, O'Reillys will have it and Napa will have a salesman that can help you. You should be able to find it in white, amber (turn and parking light), red.
I really like having the switch on the light.
Don't fix what ain't broke. You'd only see that light if you are looking up at it.