Paint them. Treadles were made in such numbers the 'value' is about what you paid for it. Aside from that, the paint can be removed if someone, 100 years from now, wants to restore it. The rust stains unpainted irons would leave on your fabrics may not come out.
If you don't want to spray paint them, a quick way to paint iron work is to use a sponge. Not a sponge brush - a sponge. Dip it in your paint then press, and dab, and smooth, to your hearts content. Wear gloves.