Part of the problem with the parts places is that you don’t know what size it really is. Sometimes I think they state that it’s 1:20, when it originally started as a 1:24 part. It’s hard to really determine the actual scale, which is why I really wish that they would give dimensions in mm or inches. That way, you could figure out what size bell you really need based on the prototype you are modeling.
When it comes to making my own stuff or buying, I try to envision how I might go about making it. If I can’t come up with a good way, I’ll buy it. But lately I’ve been making things. Before I would have tried to buy railings for my logging caboose, but I found it was stronger to make it myself. And, it looks good enough. I guess that’s the other thing; you have to decide if you will like what you build, or would be happier buying it.
It’s fun to go to some of the craft or hardware stores and just browse through the aisles; sometimes you can find stuff you can use as a base for a neat part.