Check with Lincoln Electric
They have a product called "Wearshield Frogmag" that is specifically designed for manganese rail frogs

here is a link to their catalog:
http://content.lincolnelectric.com/pdfs/products/literature/c710.pdf

Stoody has one too - for SMAW, try Nicromang to get to dimensions followed with 2 layers of Trackwear.

Also....it should go without saying, but in today's society, PLEASE read, understand and follow the manufacturer's instructions on the MSDS and in AWS Z49.1 - manganese is NOT something you want to be breathing while welding!