Does "stacked switch with two separate legs, one 3-way and one dimmer" electrical part exist?
Here is a double 3 way it will work single gang double 3 way it will work for your needs except the dimmer. One switch used for 3 way and only 1/2 of the 2nd switch is used for on off. Ok dimmer it gets a bit more expensive as you will need this style retro double digital you will also need a second switch single gang that can talk to this one similar to this single dimmer. I have not used a double with a single in the past so double check that the single wont affect both on the double.