How can I make/get a custom photo mural?

This might not be exactly what you want but I would take a look at the Rasterbator. It will blow up a image you upload and send you a PDF that you can print and assemble. Check out the gallery.

@johnpowell: thanks for pointing that out. It IS definitely an on-topic and great tool however I’d like to make something a little more professional/museum-like.

Artistic Homeowner does photo murals. You can choose one of theirs or have one made from a photo of your own. Don’t know about pricing—but it appears you then apply the mural like you would hang wallpaper. Hanging it can be tricky, so you might want to find out if the cost also covers installation. If not and you want suggestions of who can hang it, let me know. Depending on where you live, my husband might know someone who can install it.