I think that any of the shops that have bales of curtaining will make the curtains for you for a relatively small amount of money. If they don't, there's innumerable tailors that would oblige. I'm well out of touch with prices, as, other that replacing an odd piece of sun curtain, I haven't bought for a number of years.
Just one small point, are you sure that you want linen? Most of the voiles here are more nylon type composition, hang them at the window when you've washed them & all the creases drop out, no ironing required