Artrenewal.org is generally a good place to get $$excellent$$ prints, but they generally only offer prints of works they have in their collection. They counted 60,000 images last time I looked, but I didn't find Millais in their index.

It's more likely that the Tate gift shop might have, or be willing to make, a print(?) if they're the ones who have the original; although I don't know anything about their setup.

There are numerous print dealers (even Walmart again now?) but it can be hard to find one who has a specific work in stock. Since this appears to be a fairly popular one, a local dealer might be able to find one a little cheaper than the "museum quality" ones the museums generally have available.

John