I was helping my son replace the starter in his car last night…and as we were struggling to put the tubing (not sure of actual term for the part) back on, guess what it reminded me of?
(Once you have a laser, everything in life seems to remind you of it.)
What you do is measure the size of what you need and then take your calipers shopping. Liter soda bottles curve in towards the bottom so fit inside many shapes. V-8 has stuff in the shape that holds it round but if you have a bit of nichrome wire you can modify that plastic also. The small things of Folgers are also in a good range but are opaque.