I want to buy 4''*1''*1'' NdFeB magnet bars for MRI machine designing. Can anyone know some trusted vendors who sell such type of material.

 

http://www.kjmagnetics.com/custom.asp

In other words, your magnet shape should fit within the boundaries of a 4" x 4" x 2" box, with the magnetization direction in the 2" direction.

I've ordered from these guys before, just not custom.

You mention 4" in the body of your post and 14" in the heading.

 

That size in a single magnet may be a problem, you may need to stack a few to get there. But I have bought from these guys with good results. https://www.kjmagnetics.com/products.asp?cat=11

opps looks like KISS beat me to it.

 

http://www.kjmagnetics.com/custom.asp



I've ordered from these guys before, just not custom.

You mention 4" in the body of your post and 14" in the heading.

14'' length, 1'' width and 1'' breadth.