I used Redguard in my Nation Replica. It was in the banner, but I easily extracted it, changed background and shadow and zipped it. Check this post's attachment.
Only #spr1, but that should be enough for most purposes.
To get unit's Spr1:
Run Dominions II in window. Alt-Tab if it is already running and is not windowed. From visual options, put Filter off and Opacity to 100. Then choose the unit which image you want. Take screenshot (Prt Scr key after F12 in my keyboard) and paste it into graphics program. Remove DomII around the unit. Remove background. Recolor shadow. Save as targa.
If you use MS Paint, the following is the easiest way to remove the background and recolor the shadow:
Choose eraser. Choose "color chooser", and click on the black background of the image. The second color can be anything, white goes well. Use eraser with
right mouse button. It should only replace the main color with the second color, that is, background's black to white. You have to use this twice because background has two types (hues?) of black. Do the same for shadow, but use magenta as the second color. Its in lower line of colors, in about middle. Now recolor all white to pure black. The image looks almost the same, only the shadow is now magenta, but it works in the game.
Change picture's size from Ctrl-E. Save as bmp, use IrfanView or similar to convert to tga.
If the game used filter or the opaque wasn't 100, you will have many more blacks in the background. Take a new screen capture.
You could try to recolor the almost-black background to black without going white between, but might miss some almost-black pixels.