There’s a couple of gun stores in Livermore, j and r and solar tactical. Solar also has a store in Castro valley that is close to another fun store elite armory. J and R is your typical old school gun store where as solar tends to cater to what I would assume is a you get crowd with a lot more ar and ak rifles and typical accessories. He will need to go into either store and take the gun safety course which is a very easy 25 question test. Honestly with how screwed we are here in ca with the roster he will need to call around and find out who has any stock of something he might be interested in.
He may have better luck heading into the valley but I unfortunately can’t give you any insight on what would be a good place to go.
Edit: a google search shows that there is another gun store in Livermore east bay firearms. I have no experience with them.
Wherever he goes have him make sure the shop will release on an undetermined background check. Almost all big box type places won’t. CA BOF has been playing the delay game lately and after 30 days of delay your background check is considered “undetermined” the shop can release the firearm to you at that point, but some won’t.
Solar Tactical are very knowledgeable guys, mostly mil vets.
J&R have always been very helpful.
Can't speak to the other shop.
If your son is unsure about what he would like to purchase he could rent a few in Dublin or Tracy. They usually will not rent to a solo individual (suicide risk). One of us locals would be glad to go with him and let him try the gear we have. PM if interested.
+1 for Solar Tactical. Nice crew working there. J&R is where I bought my first AR (Daniel Defense). There is a fairly new shop on First St, EastBay Firearms, that has good reviews though I have not been there yet.