Hamish rule #4...match the hose to the shirt, but make sure both compliment the tartan. Lovat is a hard color to find in shirts, but you can come close with good suppliers like Land's End and Cabela's. Don't forget that you can get white cotton polos and dye them with Rit dye...play with the mixture and some scrap material until you get the color just right.

Not sure about some of the tartans you mentioned, but definitely don't wear Lovat with Black Watch.