Anyone know of where I can get a dry hood valve for a drysuit?

They normally come installed in the hood. Ary you using a "dry" hood that is attached to your dry suit or does your head get wet. If your using a dry hood like the ones made by Viking then you will need to install a dry value. Otherwise try poking a hole in the top of the hood. This will allow the air to escape.

Thanks Eric. I am using an attatched latex dry hood....where can I get a valve?

There is a place in San Diego where I have my dry suit repairs done. You could try giving them a call to see if you can have them put it in or what they would recommend.
Sea-Me Repair, 619-563-9033