dick.net is a free site where members can post and view vid clips. One of their categories is "Cumshots" (about 400 clips), with the rule that if a clip is posted in that category, the cumshot has to be within the first 30 seconds.
Here's a link to one of my own vids in that category, so you can see if it's what you're looking for (don't know if you'll have to register to see it or not, but the site is all free and legit - it used to be the old Rate-a-Rod site)
dick.net » social networking for your penis!