Large High Count Colored Aida

[Moirae]

edit: Nordic Needle's brick and mortar store closed in late 2017 and their online site seems to have stopped restocking.

Probably too late to be useful for OP, but for anyone looking, NordicNeedle has fat quarters (18x27") of black lugana in 20 ct.
https://www.nordicneedle.com/3256-720P for $16.50

They have a large selection of fabric in varying counts and canvas for needlepoint as well, but they seem to mostly sell fat quarters or by the inch (usually $1-3/inch) off rolls 40-55" wide. Like at a fabric store.

123 sells in rectangles, often in sizes 9x13", 13x18", 18x27", 27x36", 36x55".
NordicNeedle might be more expensive than 123 usually, but, if you need cloth that's long and skinny, such as 12"x55" (and don't want extra cloth left over for future projects), its can come out a lot cheaper. Using 25 Black Lugana as an example, would be ~$23 (12" at $1.95/in) from nordic, you'd have to order the 36x55" for $50-55 from 123stitch and cut it down to size (you would have lots of extra fabric though).