Our company working last 4 years using SilverStripe and we made more than a 100 projects on SilverStripe, but when we were trying to contact HeadOffice — all our e-mails were ignored and still remain with no answer. Our company is the first who started using SilverStripe in Ukraine and I guess the only company that does this on professional level.
There were quite a few requests to join the partner program! Far too many to all let in, so that's there is the community developer network. I suggest you (if you haven't already) use the developer network as that hasn't the strict contractual / business agreements that the partner program requires/
Not sure who you were emailing but the guy in charge of the partner program is firstname.lastname@example.org. It may help to contact him directly if you're dead set on a partnership!