It's been my experience that poor people don't need any help buying guns.
Perhaps your typical "poor" college student or single mother could. But pretty much every person I know who lives in a trailer (which is a lot) owns a gun of some kind, although most are rifles or shotguns.
I mean, shotguns cost $130 at Walmart. They're not exactly that far out of the price range of anyone. And if you're a person who can't save up $130 over the course of a few months, you've probably got bigger problems than defense.
Unless you're talking about pistols, which are quite expensive, IMO. It might be tough to convince philanthropists to spend $500 to give a person an item they don't "need", when that money could be spent funding medical costs or school supplies. I don't know if you've done much charity work, but it takes a lot of effort to get even $500. Most people won't give more than a few bucks, and you're lucky if you get a handful of well-off people giving you $50.
Not to sound like a Negative Nancy here, but there are other issues as well. The day someone gets killed by one of these guns (accident or otherwise) that *wasn't* self defense, people will flip their shit and find a way to blame you, which is disastrous if you're relying on donations. They'll say you didn't do a good enough job, they'll ask if you should be held responsible, and they'll basically tar, feather, and fuck you in the ass.
That doesn't even get into the black market problem. If they're poor enough to need a free gun, I'd say there was a high risk they'll fence it for some quick cash, and then the guns are going to start showing up at crimes. That's another can of worms.