The thinnest high-temp, small-quantity sheet stock I know of is at
McMaster Carr - 0.018 thick Hastelloy X. You could buy some stainless
steel shim stock at the thickness you want, but I don't know if it would
resist warping and/or oxidizing at that temp.

Dev Null wrote:

I want to buy a few square feet of 0.005 inch thick sheet to make
some parts that are about three inches by three inches. The parts
are flat leaves that slide across each other to form a shutter. I
want some kind of alloy that will resist warping if the parts are
heated to about 800F for a short time.

Can anyone suggest some place to buy this?

Thanks