I Can't Get No Satisfaction

Before I got my job at Before I started volunteering at No Limits first as a youth worker and then as a counsellor, I used to say all I want from my time on earth is to make a difference to one person.  Just one person - to just know that one persons life is easier or better because of my help. 
Then when I got trained as a counsellor and got my paid job at No Limits, that wish to help one person didn't satisfy me enough. I'd done that already.  It's a pretty humbling feeling to know that there are people living a happier life because of me.  That also sounds immensely big headed, which is something that can very very rarely ever be said about me.  So my dream changed to helping many instead.
Only now that's not enough either. A colleague of mine has a very very poorly little boy who has respite stays in Naomi House in Winchester.  He does as much as he can to raise money for them to compensate in some way for the support and respite the whole family gets from his boys stays there.  So a few months ago I decided to do something to help too.  I have a few musical connections, so decided to put on a charity gig night.  The Great Sojourn, A.dam A.sun.der and The Tiny Eyes have all been incredibly generous and offered their services for free.  I have another potential band, but they're on a bit of a hiatus at the moment, so I'm not too hopeful they'll be available.  The stumbling block has been the venue though.  Given that I'd do as much as I can for charities, in my naivety I assumed others would to.  I've contacted pretty much every venue I can think of in Southampton and Winchester to put on this gig and only one has been really supportive in their response.  Unfortunately due to timetabling issues, that venue's not going to work out.
So now I'm trying to figure out whether to go around them all and beg them face to face for their support.  Or to give up and change the type of venue I'm trying for, to something like a hall instead.  Which isn't ideal by a long shot, but potentially easier to pull off.  If I do that, it will take place and will make some money for an incredible cause.  But I won't be satisfied with it.  It won't be what I want it to be.  So do I settle or do I strive for more for my own satisfaction?
And if I pull that off, then what do I do next?  What can I use to fill this need I have to justify my existence in this world?  And is it ever going to be a satisfying answer to say that I am the reason for my existence?