I'm just wondering why there are several monthly Donation presents NOT available for purchase ? EX: January 2006, February 2006, March 2006, April 2006

Because it isn't those months. They're there depending on the month, which is why the Oct 2006 one is there :)

It's also because those 4 months don't actually have a donation present from 2006. They started doing the donation present boxes in May 2006, so those first four months don't have a box from that year, they start in 2007. Before May 2006, they just had the same box that rotated out items each month, but it wasn't a special box specifically for that month and that year like what we have now.

I get that but i've seen a couple of items that stated they were from those "Monthly boxes" so I was wondering how on earth we could get them ?

Since they would have to make new boxes for them, I believe the items periodically go out though the cash shop hustler.