Carl Pool palm food, made in TX, has several on-line sources, but mostly in sizes smaller than the 40lb sacks.

http://www.agorganics.com/products/Palm-Food-4lbs/11/254.html

you could call them to see if they ship 40-lb sacks to sellers in the NE. 40-lb sacks costs about $45 in TX.

http://www.vitalearth.com/frame-right.htm

If your palms aren't showing signs of nutrient deficiency, just feed with Miracle Gro or any other high nitrogen fertilizer. For Magnesium you can add Epsom Salts. No reason to spend lots of money on a special fertilizer if you don't need it. I use 24-14-8 turf fertilizer on all my plants and it works fine. A 50-lb bag cost me $6.

FYI, a good source on palm nutrient deficiencies.

Here is a link that might be useful: Palm Nutrient Deficiencies

Ironite is sold in New England. Its a mineral fertilizer.