There's another way to get more sugars into your brew with a limited mash tun, and that is the doble-doble method. (Another extinct brewing technique.) Basically, you mash some grain, and then use the runoff to mash-in more grain in the same tun, after sparging thoroughly. You can get to pretty high gravities using this method, though I'd recommend hot sparge water and slow batch sparges to maximize efficiency and avoiding leaving a bunch of extracted sugars in the second mash.

As for black IPA, it's a good option if you like hops. (And don't forget the orange zest or peel, which was a nice addition to the Black IPA for the Beer Fest.)

If you don't have the necessary hops, or want something less hoppy (crazy, I know, but) another brew you could try is a nice dark barleywine. In that case, adding some sugars (or other highly fermentable adjuncts) is a good idea. I recommend molasses, Demerara sugar, honey, those Indian "gur" sugars they have at the Foreign Food Mart in Itaewon... the barleywine I have in secondary now (about to bottle) was made with molasses and some other stuff and smells and tastes divine, but you need to expect a long aging period. (And I'd oxygenate it generously, as well as adding several packs of yeast; I used S-04 to good results.) You's want similar things to what Bill suggests, but less carafa (let the molasses darken it up for you). And of course it needs longer aging, though I bet my Barleywine would be drinkable now, only a few months old.

If you had more time, I'd recommend a Belgian Dubbel or Quad as another less-hoppy option, but those are impossible without a good yeast (T-58?) and usually shine more with other specialty grains or adjuncts...

I don't think we can get roast barley domestically; you can make some, but you need to wait a week before using it. (Nasty volatiles.) And unless you're ordering from abroad, you will substitute Pilsner Malt for 2-row.