You don't need one. I give you the insta, you secure it, once you have it totally secured you get him to send me the btc, then you hand the account over to him.
I'm in class or I'd help you if you wanted it.
Hope this gets done, if you're still having trouble with finding someone in an hour I'll be happy to middleman.
Ask @hope @sector @sws they may be able to help you. Be sure you have someone who actually knows how to secure for the safety of the person purchasing. Don't just ask someone you trust.