Residential Steam Heat Vent Spitting Water.

No, it is not normal. That said, before someone else chimes in, it looks as though that is -- or was -- intended to be a main vent, and it's poorly placed and even if it was working well, it's nowhere near big enough for a modern system. OK. That's off my mind.

To select a proper replacement, you -- or we -- need to know how many feet of pipe are between that vent and the boiler, and how big that pipe is. Actually getting the replacement won't be hard -- even Amazon has them, although for a variety of reasons I prefer Supply House.

However, if it is spitting water, you may have other -- seemingly unrelated -- problems: too much pressure, or not enough slope on that pipe. Since steam isn't your thing, perhaps you could post a picture of the front of the boiler, with the controls? And another, if you can identify it, with the pressure control in detail?