I've never heard of one.
I have heard of parties for kids geting their GED though. While I admire any adult who made the mistake of dropping out of school and then going back at a later date and getting their GED, I think it's ridiculous for a teenager to chose to drop out (usually for "theocratic reasons") and get their GED as an alternative to graduation. They mistakenly believe a HS diploma and a GED have the same weight. They most certainly do not.
On the college issue: You probably don't have to many graduation partys because:
1- Not many witnesses attend or graduate from college
2-Those who do, do it "under the radar"
What I have found is that when my kids where asked: "what are you going to do after HS?" and they answered: "go to college", they were met with blank stares or a luke warm: "oh, that's nice". So I think a graduation pary would not be well received.