If you are loading 41 Magnum or smaller cartridges, you can use polycarbonate tube with an OD of 5/8" and an ID of 1/2". I purchase it from McMaster Carr in 8ft lengths.
McMaster part# 8585K106. You can probably get it from any plastic supplier. If you want to load 44 Magnum, 45 Colt of 45 AR it's more complicated. You can buy acrylic tube with an ID of 14MM and an OD of 18mm, but I have only been able to find it in 1ft or shorter lengths. It's on Amazon.
I have not been able to find anything equivalent to the original Hulme tube. Maybe someone else has had better luck.