There are certain things we libertarians like to talk about, and you are right, the nuts and bolts of (private) charity aren't among them. There's several reasons for that. Others have touched on some of them already. I'll add one.
Voluntary actions are by their nature extremely particular to time and place. In a free society, one responds to problems locally, as they crop up. If there's a homeless guy on your street, maybe you try to help him find a job. But if there is no such guy, you don't (obviously). The plight of some other homeless guy two towns away is not your concern, since you don't even know he exists.
Charity is extremely particular. What is the best thing to be done depends on many factors: how much time/money/other stuff you have to give, what and who you know, and also, the particular recipient involved. Thus it is very difficult to talk about, except on a very particular, case-by-case basis, or extremely broadly. As an example, in the very brief hypothetical I used above, I said "maybe" you would try to find the homeless guy a job - but then again, maybe not - maybe he has some cash, and what he really needs right now is just the directions to a cheap motel. Or maybe... or maybe... etc. There are infinitely many possible scenarios here.
In contrast, the things you see talked about a lot here, e.g. gun rights, tend to be nice and cleanly defined problems. Rights are like that: easy to define, easy to think and write about. We can predict with high confidence how gun laws would be in a free state, because we have a broad and powerful theory about gun rights.
Charity isn't like that. So we don't end up talking about it so much.