Hello, my pre-lit tree has this fuse bulb in the string lights. Balsam Hill calls them master bulb. I have not been able to find where to buy replacements (Balsam Hill does not sell them and does no share where one can buy them). Some other christmas trees use them as well.

I’m hoping someone would know where to buy replacements for them? A picture is attached. They have a gray base with the actual bulb inside a plastic casing. Thanks in advance!