As it turns out, one of the people in the local Belegarth group is the owner of Edhellen Armoury, so he was able to answer the question I posed in my previous post.
The answer is that different groups have different standards for stabbing tips, so a stabbing tip that would pass inspection and thus be legal on the field at this group won't pass at all groups. So if they were to advertise on their web site, then they might end up selling stabbing tips that wouldn't pass. But when I called, they knew I was in the area because I had come to Belegarth the previous time, so they knew that their stabbing tip would be legal here.
And in case you're wondering about the title of this post, it comes from the book "The Color of Magic" by Terry Pratchett. It means "economics" ("reflected sound" = echo, "underground spirits" = gnomes, so "echo-gnomics")