I got a Marmot fusion 30 In XL a few years ago (down inner primaloft outside) suitable down to something like -1C. It is supposed to be for up to 6'6" but I am 6'5" and I woke up with my arms folded above my head inside the hood and my feet were clear of the foot. Don't know how they measured the 6'6" max user dimension but they were wrong by what must be best part of a foot.
Don't sell them anymore but I am guessing that any Marmot bag in their XL dimensions would be the same.
Another solution is to try any of the main manufacturers but contact them, their distributers or their major retailers and ask for the max user sizes of their XL versions. Most big names will do XL bags for a premium and major retailers would be able to special purchase them (perhaps for a special purchase fee).
Another idea is try Golite. They do rather nice and light bags and quilts. I got one of their quilts in XL and it covers well over my shoulders without my feet being anywhere near the foot, even with my toes pointed. No hood on the quilts but a good baffle and hood on their bags. My quilt was £100 in a sale but you won't find one for anywhere near that price. Good to -7C too. Wear a hat or balaclave though.
Seriously have you asked about XL in any of the usualy makes? ME, TNF, Rab, Snugpak and Marmot?? They mostly do them to special order.
Another option if you want seriously good kit that is light and highly specced is PHD (Pete Hutchison Designs). They do a "Design Your Own" service for a premium. You can design it to your exact specification and if this service doesn't allow for one long enough for you (it will) then call them. All bags are pretty much made in UK to order so you order it and they make it how you want. They are a little bit like Aiguille Alpine in that they are a kind of cottage industry but a bit bigger.
BTW Pete Hutchison was one of the early designers at ME who through his talent for designing gear and clothing, particularly anything in down, became one of their top designers. He left them and set up PHD to focus on the best designs and materials to achieve lightweight products. Basically that is what their focus is. Once got told that PH has forgotton more about down bags than most of the current designers know!!
PS PHD has a sale on now so you might be able to buy an XL minim 3 or 5 at cheapish prices. These are good spec bags that are only available as design your own normally. Most PHD bags have 200, 400, 600, etc numbers but these 300 and 500 are kind of more practical temp ranges. Seriously, look at PHD sales as they often offer the XLs at about £30 more than the standards. If you call them I am sure they would let you know if the XL is big enough. If not then work your charm and they might make an XXL in one of the sale bags and not charge you much for the special. I know someone who called and asked for a special in one of their sales items and they made it up especially and it arrived about a week later.
official length is 198 cm which is about 6'6" but it is generous , rated down to -6 ( I have used it in a snowhole in Cairngorms quite happily) and RRP around £80 but occasionally can be found for sale as low as £40 which is what I paid for mine 
