Most rv bulbs are found at your local automotive. Sorry I don't know the one you want. It could be 1383?
clicky for exampleBulbs: I was going to start a list of what people have used to replace bulbs in their TT. I had to replace the one over the entry door outside.
The bulb is #1003. It is rather dim IMHO. Before I found that one I had a quick run to Walmart and found one which was almost a perfect match, same size just stronger, #1156 (automotive area). We're still using that one and it seems to be working well. We don't run the outside entry light for very long and not overnight, so I'm not sure if that will overheat. Maybe an electrician here can say if there is a problem with this.