I should have posted this earlier but forgot about it. If your local
Lowes has a bunch of discontinued stuff on sale they may have these
mullion kits. Item #92957 72" Mull kit 20,25 series

This doesn't apply to the smaller kits on closeout.

I couldn't care less about what they are made for, but each kit contains
a piece of 1/4" x 4" x 5' piece of high quality aluminum plate. To buy
the aluminum would cost about $30 to $40 retail and the kits were on
closeout for $1.07 each. I bought all I could find in my area and all I
wanted was the aluminum so if anyone wants the plastic strips I just
need a little something for my time and then shipping.

The kits are so you can cut off the nailing strips and mount the windows
closer together.

If you happen to weld or can use the aluminum somehow it's one hell of a
buy if there are any left! You can even call ahead and ask if they have
that item number in stock (Item #92957).