Surprisingly enough I found it at Joanns. It was in the taffeta section with a label that said 100% Polyester Black Lining. I believe it was $4 a yard, but with a 50% coupon was only two bucks a yard. It feels very similar to the WBBB 1.7 layer material, except it has a bit less stretch and seems to lay flatter for me.
Also known as dress lining. Ask at the front door, and they'll point you right at it.
Where did you find the WBBB pattern? I've made a number of hammocks, and would really like to try that one.