As much as I hate it when the Chinese steal American designs, in this case the originator no longer wants to sell them. There are several outfits selling clones on Ebay, in a variety of colors and prices. I have Travel Agents on several bikes and just ordered a set of these. I don't find the Tektro road bike, V-brake levers comfortable as they are too narrow for me.
Road Bike V Brake Adapter Converter

I've known the owner of Problem Solvers (and QBP) for over 40 years and the next time I see him I'll ask why they were dropped. My guess is fear of lawsuits. Or actual lawsuits. For people like us, they aren't tricky to set up, but not everyone is mechanically inclined.