First up, purple is not magenta, those ones show up as pink, and you either have to jump through hoops to make it or buy one for (usually) 6 figures off the market.
Purple was available for 250k to rep and 125k for imp till patch 1.2, its probably too little too late to tell you that you should have gotten one then, but you options now are this.
1: GTN. There will be some for sale sooner or later, if you have money you are prepared to spend this is the easiest.
2: Artifice. I can't personally confirm this, but apparently the schematics (and many others aside) should be available through treasure hunting crits. I have been able to find precious little information on this myself so if anyone can give details here it would help.
That's all I know on the subject at this time, good luck.