I found some decent replacement laces for my chuck 70s on eBay. They're not exactly the same, but close. The new lace is on the left shoe, old lace on the right. :
Replacement Converse Chuck 70s High Top Laces Extra Long 72 - Etsy
Unisex Converse Chuck 70 Laces 45 Inch Egret
Replacement Converse Shoe Laces – FEEL YOUR SOUL
Converse Classic Chucks vs. Chuck 70s: Which Pair Should You Get?
BLACK Replacement Converse Chuck 70s High Top Laces Extra - Etsy
Amazon.com: ZHENTOR [2 Pairs] Flat Athletic Shoe Laces - Cotton Shoelaces for Sport Canvas Shoes and 70S Replacement Sneakers (31in, Beige) : Clothing, Shoes & Jewelry