It's not your imagination. Much like SF, NYC is a gay mecca where gays can grow old with dignity. The number of older gays, therefore, dwarfs the count of young twinks and makes them seem less scarce. In absolute terms, there are definitely more twinks than in other cities, but they are harder to find and are often very occupied. Your best bet is going to be to make offers on Grindr. With this approach, you need to play volume and expect a 5-10% response rate because many will think you are scammer who's going to ask for their bank account info. The rest will quote a high price or just toy with you for no reason. A small percentage will be serious. Beyond that, your best bet is going to be seeking.com.
The shortage of twinks in NYC is so acute that I'm planning to move to Chicago to live right next to Northwestern and Loyola universities. Godspeed.