There are a couple of optional vendors who will sell weapons in general and my weapons specifically. These vendors will always have at least one of every weapon added by the Mega-Pack in stock with every inventory refresh period.

Vlad Fallout: New Vegas

Reginald Tale of Two Wastelands

These vendors specialize in certain types of unique weapons from the Mega-Pack, and are the only legitimate way of obtaining them without console commands. They were split off on their own so that if you don't like wacky or supernatural weapons in your game, or find them immersion-breaking, you can simply choose not to install these vendors and never encounter those types of weapons during your playthrough.

Dr. Quarton Fallout: New Vegas (Wacky & Sci-Fi Weapons)

The Bronze Oracle Fallout: New Vegas (Occult & Supernatural Weapons)

These automated vendors provide 24-hour access to supplies and provisions that might be needed at a time when the dedicated store is not open for business.

Amm-O-Matic Fallout: New Vegas Tale of Two Wastelands (Conventional Ammunition)

Maude's Fallout: New Vegas Tale of Two Wastelands (Weapon Mods)