Beard Balm of some sort to ease the itch during the initial phase of growth. Beard shampoo/conditioner and a good beard oil will help with brittle and overly sheddy beards once you reach "full beard".

Also, be aware that (at least for me) there are two "itchy" stages. First is the immediate itch of the first couple weeks. Once the hair gets long enough to lie flat against the skin, this should go away. Second, is the point at which the beard hair gets just long enough to start to naturally curl. This is usually the longer "itch period" for me. It will last as long as it takes for the hair to get long enough that the curled ends no longer reach the skin.

Again, decent beard shampoo/conditioner and beard oil can help soften and tame the hairs so that the irritation is either significantly reduced or eliminated. Just make sure that when oiling, you don't overdo it. Also, using a beard brush to apply and spread the oil helps as, if you work the oil all the way down to the skin, it will help exfoliate as well.