I looked on NAP's website, it does look like they quit making the Spitfire Maxx in 125 grains, must have just happened because I bought some 125s this past weekend. As for replacement blades, I do believe they are different, on the website they're a different product numbers. I haven't bought replacement blades ever so I'm not absolutely sure.
http://newarchery.com/publish/posts/75/new-125gr-spitfire-maxx-amp-bloodrunner-2blade.html i emailed NAP to see when replacements would be available
they are available, part # is 60-693. So it looks like the replacement blades are the same for 100 and 125
You are correct - the replacement blades are the same for the 100 and 125 grain Spitfire Maxx broadheads. The only difference between the two heads is the additional weight of the collar on the 125 grain version. Other than that, they are identical.
nice hit!! the spitfire maxx are my favorite broadhead. i have yet to loose a deer with any spitfire product