Have you tried doctoring up some curry roux from somewhere like HMart or another Asian grocery store? I've tried almost all of the House Brand or S&B Brand name curry roux I can find and they're all pretty tasty, if not just a tad bit salty when made as directed.
Basically they are blocks of curry that you melt in the liquid of choice, usually water. I'm wondering if they might provide you with a good non-grainy base curry to work from. Take one small block (or a piece of one) and dissolve it in some hot water and you have an instant curry sauce.
Again, I'm not familiar with the Melting Pot's sauce, but the boxes of roux are cheap, and if it isn't exactly what you wanted, it's mighty tasty anyway.