If theres a specific card that you want to add to your deck, you can usually buy it from online markets or gaming stores
"If only I could go back in time I would spend all my money and buy 10 Tarmogoyf when it was first released, I would be rich now"
But given the nature of the card, dead late, terrifying early, it's a no-brainer that 3 would still be the preferred number if legal
Promos (P) Promotional cards - like the aforementioned Lightning Bolt from MagicFest - can come from events, prereleases, special products, store promos, conventions, Secret Lair drops, and various other places where Wizards know we players are willing to pay top dollar for them
Shipping Times We also have the best turnaround in the industry