Williams used to carry a Maris Otter extract, but I don't see it on their site any more.
They do have a "pale ale extract," which is "mashed from the finest two row European pale ale malt, and is ideal for English and American style Pale Ale and Bitter. Compared with our German Pils extract, this one has a slightly darker color and a hint of caramel in the malt flavor. An aromatic, rich flavored pale extract with a 'just mashed' character for ale and IPA styles."
Is this Maris Otter? I would expect that if it was, they would say so, though I have found them to be exceedingly unhelpful in the past when asked about what sort of malts they put in their various extracts. But maybe it would work better for you than Alexanders, et al.