This can easily be obtained through the use of the safehouse vendors. Collect and use your scrap to buy weapons, food, vehicles etc.
If however, your safehouses glitched like mine did and you find all of your vendors disappear, this can also be obtained in multiplayer by using the vending machines to buy your weapons etc. This is the method I had to use due to the bug that still hasn't been fixed as of Jan 4th.