Why are there so little guns hidden around the city in gta4? This is the problem of gta since SA, there is nothing to find in the whole wide world. Everything is in stores. There is nothing in the allies or the rooftops. I'm also having a bit problem with money. I'm doing missions for Faustin now and I only got like a grand in cash. What are some was ways to get cash?
Do taxi missions, ambulance missions, or pizza delivery for extra cash. Oh, wait, no... they took those out for IV.

I know! Do the drug trading game, because that nets you mad cash, is fun to play, has varied gameplay, and gets you a new outfit when you finish it. Oh... sorry, no; that was Vice City Stories, only.
The alleys are as empty as you suspect. If you want to find stuff in the current Liberty City's alleys, buy Chinatown Wars on the DS.
In GTA IV, there is a bulletproof armor right near your initial base, but getting there is a huge PITA until you get really comfortable with the controls. Use youtube to lookup armor locations, mark them on your map, and take an insta-cab ride to them instead. That gives you armor before the game unlocks it in stores, and saves you half a G even after it becomes available for purchase.
There's a rocket launcher on a rock off the north shore of the center island. You have to swim to get to it, but it becomes available LONG before the story lets you buy one.