I have been working on cloning a recipe for the Biscoff cookies for a while because everybody seems to love them and homemade always tastes better than store bought. I have written an article on the Desserts site which will be coming out later this year, but you can access it early in the Desserts archives (go to the archives and search for "Biscotti vs. Biscoff and Recipes for Both"). I am a flight attendant for Delta Airlines, so I have access to those cookies more that I would like. I had fellow flight attendants taste my tests, and while there are actually better and fancier recipes for speculus or Speculoos (which is what the cookies actually are called - they are traditionally made for Christmas in The Netherlands and Germany), the one I finally published is very close to the Biscoff brand. European bakers tend to bake their cookies longer than we do in the US, and the other flight attendants agreed that the overbaked ones were closer than the less baked ones.
Several grocery stores carry the Biscoff cookies, Walmart, Target, and Smith's in my area.