After much debate I found seat welp at a great price! 1/8" bead.
$11.75 for 10 yards shipping included.
According to the description the guy is liquidating his business and has lots of colors.
The notes of the page say to put notes of what color you want in the message when you place the order. He's probably got a lot left he just lists a quantity of 1 for some reason. Certainly worth contacting them first though.
Welting is a fabric covered cord made of bias-cut upholstery fabric. Welting is sewn with a fabric lip so it can be inserted between fabric pieces, and is often used on the edges of arm rests and seat cushions. Welting is also called piping. It can also be made of vinyl as a separate insert piece to be used in automotive upholstery between vinyl panels on seat covers or door panels.
Cording is usually an undecorated circular cord used to create the rounded shape of welting. The fabric that constitutes the outside of the welting is sewn around the cording to give it a 3-dimensional quality. Cording comes in a variety of thicknesses, from string thickness to 1-inch or thicker cording for upholstery items.
This stuff is vinyl welting...
Remember that I owned a custom auto upholstery business in the early 80s...