I've bought quite a few products off Heritage of Scotland and they've been good quality and made in Scotland. My Argyll jacket is one example
I've also ordered my kilt through them - as they also hire a traditional kilt maker (might be worth keeping that in mind... that they're keeping a skilled traditionalist in business) and they order the material from whatever mill you choose.

They have 6 shops in Edinburgh and supply about another 10-20 shops in Edinburgh, Glasgow and Fife. They also have quite a few ebay accounts - not just Heritage of Scotland but the ScotlandKiltCompany is one where I bought some accessories and probably around 5 more with offices based all around Edinburgh and Fife.