I can't help you with purchasing those sorts of items from websites.....because I never used those things. But what I DID do was that I would improvise on my own to create low-carb versions of things.....though to be honest, I tried to avoid anything sweet or anything that would kick-in any sort of cravings.
But for a barbecue sauce....if I'd decided to try and make a low-carb version....I'd have probably taken some plain tomato paste, added a bit of splenda and a tsp/tblsp of vinegar....and see how it tasted. And then tweak it a bit depending on taste.
You pretty much have to accept that it's rarely, if ever, gonna taste like the real thing.....just for starters. Honey, molasses and brown sugar are verboten, right off the bat. And tomato paste and vinegar would be something you'd have to use in very small amts....and even Splenda, for that matter....as they're not totally Atkins-approved....and you'd certainly not want to use them during Induction.
To tell you the truth....I did the best when I stuck to whole foods and totally avoided any of the processed low-carb items they sell in stores or on the internet. You can adjust very quickly to living without them.