DNA ladders for large fragments

Hi all,

We are working with about 10kb DNA fragments and are having difficulty locating a suitable ladder. We'd like to use a ladder with perhaps 5, 10, and 15 kb markers (with increments of 5 kb if possible).

Does anyone know of a manufacturer for such an item? OUr usual vendors, while they have larger bp markers, do not have wide increments between the bands.

Thanks,

Les