I am trying to find an 8-inch deep root barrier to put around my aggressive Amity raspberries.
But I cannot find this locally or even on amazon.
Does anyone know of another way to stop the suckers from spreading?
Short of digging them up regularly to thin and maintain the roots, you'll need a physical barrier. Personally, I recommend using something that is non-toxic, which means no landscape timbers, treated wood, RR ties, etc. Instead, choose redwood or other high tanin wood, the tanins help stave off rot, should last 3 to 5 years. Or, choose cement blocks, pavers, or corrugated roof panels (fiberglass, aluminum, or steel ).
I would also recommend going considerably deeper than you think you need, roots have a way of hitting a barrier, then following it until they find a way out. If you think you only need 8" depth, go at least 16" deep, then you know you'll be safe.
No matter how you look at the above solutions, it will be costly in materials and especially in labor. Be prepared.
Look into the use of copper sheet material or copper mesh.
Root will not pass thru the copper.
In the past I've used corrugated fiberglass roof panels for this, thin ones work better for tighter radius. Seems these have gone over to PVC at the 'big-box' stores but it should work as well. Use a side-grinder to cut it; saws tend to shatter the PVC.
Thanks for all the suggestions.