I'd guess they exist, but a quick search turned up only an RGB color-changing version of what you want. I.e. instead of fading in and out, it just slowly shifts through the rainbow.

Are you set on a self-contained bulb. The Internet is full of example projects, mostly using the classic 555 timer chip, to fade LEDs in and out. Depending on how the bulbs in your machine are wired, you might even get away with a single timer circuit for a whole array of bulbs. But barring that, as long as it's not that many bulbs, you might find it acceptable to just create enough copies of the circuit to wire up each individual bulb with one.

With the right combination of resistors, capacitors, diodes, and the 555, you should be able to create just about whatever lighting effect you want.

Alternatively, for a higher expense in hardware (though not much) and IMHO a slightly more intuitive approach, you could use an Arduino controller. Depending on the exact microcontroller, i.e. how many I/O pins it has, you can set one up to control many lamps, and while learning the basic Arduino ecosystem isn't trivial, the actual programming is probably easier to understand than trying to figure out resistor and capacitor values that do what you want with a 555 circuit. In Arduino, you can just set up a loop that explicitly sets the LED brightness to whatever specific value you want over time.

Granted, none of this is nearly as easy as just finding an LED already designed to do what you want. I've never heard of such a thing, but I'm far from an authority on the subject. If no one else here has any ideas, maybe you just have to do more web searches, or post in different forums that are more dedicated to electronics and/or LEDs specifically. In a pinball forum, it's a pretty niche question, but in an electronics forum, it might be borderline FAQ.