Thanks for your helpful replies everyone. I have looked at the VOID figures, and they did not do much for me. Some Warzone miniatures might work, but they are quite expensive these days.
I may just hold out for that plastic boxed set, but in the meantime, I think I will try a small conversion of a five-figure unit.
This is what I am shooting for:

I have extra Void Interdictor troops unassembled, so I may borrow the bodies, legs and arms of those:

(image from user Bagpuss)
The backpack units and bolters could be borrowed from Space Marine bitz. The winged shoulder plates could be borrowed from the Gangs of Mega City One ganger set.
I am not worried about all the flowing material. It's not something that makes much sense to me (all that flammability?) so I could omit it and just green stuff some symbols and purity seals.
The head will be the biggest challenge. The only female heads I have (and that I am aware of being available) are the old Dark Elder heads. I could trim the hair and sculpt on my own.
Alternatey, I could use female Eldar Guardian bodies along with the Space Marine bitz.
Either way, I will try to snap some pics and post here as a follow up. Thanks all!