I've been preparing my leather tutorial, so here is the lace entry.
Weaver leather (
http://www.weaverleather.com/contract/index.html)
sells an item called Alum Tanned Lace Sides. It is a Chestnut color (item # 06-700s)
It is 5-7 oz leather and the hides are 21-25 square feet at $4.22 per sq ft.
It is perfect for those Horween "Heart of the Hide" gloves from Rawlings.
Weaver only sells to business accounts I believe. They have a catalog but don't sell online.
Siegel Leather of California (
https://www.siegelofca.com/) also sells hides called Red Lace and Black Lace.
Both are 5-7 oz hides. I haven't seen these hides so I can't vouch for them.
I also buy real baseball leather from Siegel.
It's stiff as a board, but once it's been soaked, it cuts easily and makes nice, pure white laces which can be used as glove welting.
I'm sure it can be dyed although I haven't done that.
Generally, alum tanned hides are used for making laces. Get them good and wet before trying to cut laces.