They have 108" "mottled black" at Bear's Quilt Shop here in CA.
http://www.bearsquiltshop.com/pages/ucCart/product.asp?reckey=5093
Their fabric is NICE too. You might email them & ask if they have plain black if this one won't work (or you can't find one closer to home!). I got a beautiful deep claret red backing from them a month or so ago.

There's a textured solid black 108" here:

http://aaaquilterssupply.bizland.com/store/page43.html

you may have to copy and paste this since I don't know how to put a link into this board.

:)...Rae in San Diego

Hancock's of Paducah has a solid black 117" wide backing by Robert Kaufman at 12.98/yd
http://www.hancocks-paducah.com/Item--i-RK-INF-BK
and moda marble jet black 108" wide backing at 12.98/yd
http://www.hancocks-paducah.com/Item--i-M-11002-11

I have used both of these fabrics in 44" widths and, in fact, buy them both by the bolt (from this supplier). Moda marble is a heavenly soft fabric but is not truly solid black. It is marbled with gray. It works well with batiks, but you will lose some of the drama you would have with a true solid black contrast.

The Kaufman line (Kona cotton solids) is a heavier weight, more like broadcloth. It is quite nice and plays well with standard quilting cottons nonetheless. I would be happy to send you a sample of both.

I bought the fabric for my first quilt at fabric.com. I'm not sure what others think of them, nor do I have anything to compare it to, but it seems nice!

Anywho, they have black, 108", 100% cotton broadcloth.
http://www.fabric.com/quilting-fabri...-br-black.aspx

I have seen backing @ keepsake quilting.com. Good luck

I bought my first wide backing from Fabric.com too. Prices are good. First order ships free.

Godess:
You might try FABRIC.COM (use lower case). I've seen 108 inch fabric on their site. Good Luck!

Try this website http://www.marshalldrygoods.com/index.htm

They sell 108" wide black cotton backing for $3.99 a yard.