I contacted Anycubic about how to purchase their new filament sensor that's on the new updated ultrabase model of the i3Mega. Turns out it's another 3d printed part like the original sensor so they just sent me the stl files. Just take the parts out of the original sensor and put them in this new one. Only problem is you need the magnet and the little metal ball connector Anycubic used to connect the two pieces. Since I didn't have those parts, I just ordered some magnets from ebay that seem to do the trick. I used one magnet in the part that screws to the frame and two on the sensor for extra mag power. I attached the two magnets to the sensor with a round headed M3 12mm screw.

UPDATE: I just found this threaded metal ball which is what Anycubic uses to connect the sensor to the magnet mount: http://www.ebay.com/itm/12Pcs-M4-10mm-Threaded-Steel-Ball-Rod-Ends-For-3D-Printer-Magnetic-Joints-/391365608649?hash=item5b1f3544c9:g:VhIAAOSwKtlWjgqK

Here's where I ordered the magnets.
http://www.ebay.com/itm/20PC-N50-Strong-Countersunk-Ring-Magnets-12-x-3-mm-Hole-3mm-Rare-Earth-Neodymium/271502565580?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649