Welcome to the forum.
If you are having a problem finding a retailer, you can get it directly from Bradley.
I just read your other post. If this post is referring to the same fuse, then that fuse on the back of your generator is not referred to as the in-line fuse. That is a glass fuse, which I believe is 10amp. You can find them in almost any hardware store, or auto parts store. Generally to remove the glass fuse, that cap either screws off, or you need to depress it, and turn it until it stops, then pull it out. The in-line fuse that we refer to on this forum, is the in-line fuse that is located in the back of the cabinet.