PM's have long been granted only to paying memebers. Many many years.
As for why people aren't selling to you, sellers can sell to whom they wish. Myself, I used to hold to the "First 'I'll take it gets it" rule, but more recently, I've sold to the first one that I feel comfortable selling to. You have only a handful of posts here and no iTrader feedback. If it was a choice between selling to you or someone with plenty of feedback, positive comments in GB&U, or even better, someone whom I've transacted with before, they'd beat you out even if you were "first". It's not a reflection on your character or anything, no offense is intended at all. People that sell/buy a lot may unfortunately eventually deal with a scammer or deadbeat or flake, and there's been a lot of them here over the years. Someone with history will be put in line before someone with none. Therein lies the rub, I guess. Can't buy because you have no feedback, can't get feedback because you can't buy.
Do you have any history/feedback on other forums? eBay, gunbroker, swappa, etc? If you do, you could cite those as references.