All of my suits and sports jackets have been tailor made. Odd trousers, on the other hand, are usually OTR, as are about half of my shirts. For cords, for instance, I don't see the utility of custom-made, where OTR will be perfectly serviceable at a fraction of the outlay.
It's not going to happen. Even if you could identify the manufacturer and the bunch, the colour would still likely be different due to minute differences in the dyeing process. Better idea might be just to have some snazzy black tie-related trousers whipped up, in a Black Watch check for instance.