Sandipex is held monthlyhttps://sandipexstampexpo.com/
This website only shows a few dates. Go ahead and call to confirm the next date. There should be a few dealers there that can give you an idea of the worth or your collection, and how to dispose. I have also donated quite a few stamps, and taken a healthy tax write-off. You can always post a few of the earliest (oldest) stamps here so that we can give you a quick idea of what you have. Good luck.