So I have thought of almost the entire progression for my trio that goes from D minor to D major. Here is what I have of it so far:
D minor -> C major -> B minor -> ??? -> A major -> D major
And here is the harmonic relation:
i VII vi ??? V I
And here are the respective key signatures:
The C major can be thought of as D dorian, at least at the beginning of the section that has that harmony because of the C -> D motion. But this goes from simply being D dorian to being full blown C major. The C major -> B minor motion is where the key change occurs from 1 flat to 2 sharps.
Thing is, I have no idea what harmony to use to bridge the gap between B minor and A major. On the one hand, I could simply not have this bridging harmony and go from vi to V directly. But on the other hand, I am wanting this bridging harmony because I want to reserve the dominant chord for after D minor appears for a third time. Overall this is my harmonic plan:
Dm ---> Bm -> Dm ---> ??? -> Dm ---> A -> Dm ---> D
As you can see, I have D minor occuring 4 times. The short arrows are to represent the sudden appearance of D minor which in my piece represent cold snaps. The long arrows are to represent the chord progression going towards D major which gets longer each time before D minor suddenly appears again.
So without using the tonic major early on or going directly from vi to V, how can I bridge the harmonic gap between vi and V?