+1You can use two-row, and maybe try toasting a couple of pounds of it, to sort of emulate maris otter. It won't be the same, but it would still be very good in a stout!
i'd say don't over complicate it - just use the two row. in something like a dry stout, i think it would be difficult to distinguish one base malt from another.
I will say that I am seriously considering roasting base malts exclusively as it gives the house a wonderful smell.That makes sense. I'll check back for your result. I have 2 lbs of 2 row in oven at 250 right now. Letting it go 25 min.