I make parts for Tightspot and can say they are definitely the way to go, but in the meantime you can get some small sheet metal screws and screw them into the rubber between each arrow and tighten up your existing quiver just like the adjustable wedges on the Tightspots. You might need to try some different lengths and or grind them just right, but I know for fact that it works.
It's not the perfect solution, but does actually work quite well at keeping smaller diameter arrows into a quiver not perfectly designed for them.
Cheers,
Pete