Would be a shame to do without that delicious cocoa butter, which, historically, is actually the most expensive part of chocolate! I can't believe that if you can get those fancy brands of unsweetened that bittersweet isn't available. Have you looked at sweets suppliers, or that section of your grocery store, rather than the baking section? Lindt is generally quite easy to come by and has a range of intensities. Basically, you're just looking for a very dark, high solids chocolate bar. I think the standard for 'bittersweet' is 35%, but I'd be more inclined to use 60-80%, depending on the recipe. The higher the percentage, the more apt to seize, I think.

As for the curry, I'd suggest using marshmallows instead of jello with the chocolate. Hot chocolate-based sauce and gelatin do some weird things when combined with the copious quantities of beer required by curry-consuming Britons...

Nestle says that 1 ounce of bittersweet chocolate is equal to 1/2 ounce unsweetened chocolate plus 1 tablespoon granulated white sugar added with the rest of the sugar in you recipe. (Bittersweet chocolate has had cocoa butter added to it, where unsweetened chocolate has almost none, which is why you don't substitute one for the other ounce for ounce.)

Both brands of chocolate are very, very good, and it would be very hard for me to pick which one is better. But there's also Ghiradelli and Guittard, which are not only widely available, they're less expensive, and they're very, very good too. I've used them all and like them all.

Chocolate curry. . .hmmmm. I'm not sure about that, but my mum thinks chocolate vindaloo might be possible.

I've used Lindt 70% from their Intense Dark Chocolate candybar line for many desserts, frostings and sauces. It has very good flavor, snaps (from good tempering) when you break it, melts very nicely, and is very smooth with good sheen.

Cooks Illustrated did a taste test of dark chocolate and gave the Callebaut Intense Dark Chocolate (60% cocoa) the nod as the best. The next in line was the Ghiradelli Bittersweet Baking bar (60% cocoa). The 3 other recommended ones were: Dagoba organic semisweet, Michel Cluizel Noir de Cocoa, and Valhrona le Noir.

I'm no professional, and I couldn't say which is better between the two having never used them; if their other products are any indication, I'd personally give the nod to Valhrona but not by much.
The conversion might be a little tricky to do, but bear in mind that most companies' bittersweet chocolate is about 60-70% cacao, w/ the rest being mostly sugar. Since you're starting w/ 100% cacao, I'd go with around 1/3 sugar by weight to split the difference. So, if, for example, your recipe calls for 3 oz. bittersweet chocolate, I'd cut back to, say, 2 oz. unsweetened chocolate, then add 1 oz. sugar. If you can't weigh your sugar, I'd estimate that's about 1 1/4 tbsp. (7 oz. sugar = 8 tbsp (aka 1 cup)). [Semi-sweet is even more sugar, FYI.]
And I've never used unsweetened choc. in curry, but I have used it in mole and chili and it works like a charm, so I'd say why not!