M.F.
Hi D.,
I'm sorry to hear about your son's hearing loss, and you are definitely on the right track with seeking out services for him. Keep on top of regional center. They can be a great assistance for services, but sometimes really need to be prodded.
As for teaching sign language, I found the best way to do it was to simply start demonstrating the sign for the object every time I gave it to my daughter. I started her at 6 months when I got her (I'm a soon to be adoptive parent) and for me, I only focused on the necessities such as milk, water, food, and more to begin with. Because of his age, and his potential on-going need for assistance in expressing himself, you might also think about adding the words: help, please, thank you, and other things you see him needing daily. There's a great basic sign book which I think is called the Joy of Signing, and also introductory videos. I would encourage you to really start with the words that you need him to know in order to reduce his frustration.
For example when you give him milk, sign milk as you hand it to him, and then sign it a few more times. Be sure to respond when he begins to sign back (with a big smile,etc.). Once he begins to have the ability to express himself his screaming should be reduced. Also you can spend time with him just playing and showing him different signs for things. As frustrating as it is for you, it's equally or more frustrating for him not to be able to be understood. Also, don't worry if he changes the sign at first. As long as the two of you understand each other, that's good. However, if you think he's going to need to sign on-going, you might want to continue to show him the correct sign to encourage his ability to communicate with others as he gets older. I'm sure there are sign classes and those who would assist in teaching, but you can ask about those services through regional or your insurance perhaps.
I hope this helps and good luck. Also make sure to get some support for youself. I'm a single mom, too, of foster/adoptive kids and they have some additional needs too, so you want to take care of yourself!
M.