There will always be availability.
Its absolutely impossible to tell and you'd be guessing, but out of the 350 + million firearms in the U.S, how many would you say are illegal ?
You do realise that so far thew authorities have said that the weapons found were legal but were altered illegally right?
Of the last 4 big incidents in the US 3 of them the weapons used were owned by the shooter or they had access to them via family members.
The thing that was illegal in 2 of them including last nights was they were altered.
One of the others was the person may have been mentally ill and had no business having access to firearms.
Not sure where this whole argument about illegal firearms started but it doesn't matter. In the majority of the incidents in the last few years curtailing access or stringent access may have helped.
Tougher ID laws, How many you can purchase, the types of weapons that can be purchased etc... small things like that would have helped here possibly.
Yes he may have turned to the streets but honestly how many people know how to buy from the black market? And would the black market sell to him in bulk?