I am looking for the (a) manufactor of the braided leather used for
Bolo String ties, not a Bolo dealer but the manufacturer of the
leather string.

Greetings!

I recommend that you contact the Tandy Leather Company.  With over 100
years of experience in leather craft, they are experts in their field.

You can reach the Tandy company by visiting their website, or by
calling toll free, 1.888.890.1611, weekdays 8 a.m. to 5 p.m. CST.
http://www.tandyleather.com/DEFAULT.ASP

The most economical way to buy leather is to purchase it exactly as it
is received from the tannery. This form of leather is usually priced
by the square foot and sold as a complete hide.
http://www.tandyleather.com/leatherprice.html

Types and sizes of braiding materials will vary with each project. 
Here is a link to some examples of braiding material available through
the Tandy Company.
http://www.tandyleather.com/searchprods.asp?searchstring=braid&pagenumber=3


Search strategy:

I was familiar with this company