I get brown sugar twin at my Albertson's market, too--- I like it a lot! Usually a low carb/health foods store (if you have one in your area) will carry it. You might also search for it online--- I know a lot of people that have gotten hard to find low carb stuff this way.
Sweet-n-low and Twin give me a headache, so I haven't tried either of their brown sugar substitutes...does anyone else have the problem, and if so, have you tried the brown sugar sub? I wonder if it would give me the same reaction?
Dr. A mentions in the SBD Cookbook that there is a Splenda liquid brown sugar sub. that you can buy online.