In the interest of never having to track down the exact replacement blades for my DEWALT 25mm Cartridge Blade Snap off Knife model # DWHT10250 with 25mm laser-deposited tungsten carbide (oOoOoOoh~) edge, please find below links to the 5 (DWHT11925) and 20 (DWHT11925F) packs of replacement 25mm snap-off blades.
Local hero AvE tears down and tears into the gimmicky tungsten-carbide coating which is typically used to make drill bits extra hard but is virtually useless at prolonging the longevity of a rough-and-tumble shop knife like this as its failure tends to stem from chipping of the blade edge which is not improved whatsoever by the additive.
It's not immediately clear how to reload one of these gadgets if you've not had to in years (or just never read the manual, as the case may be. but surely isn't...). These knives have the unique feature of being automatically reloadable; once a blade has been fully spend simply remove it by sliding it all the way off the end then return the slider to the fully retracted position, past the notch in the blades. Sliding forward once more catches the next blade in the cartridge, assuming there is one.
Now that we have our new blades the mission is not to install one that is active and pack a few into an onboard storage slot, as it is with virtually every other knife of this variety. Instead remove the blade cartridge by depressing the black tab and sliding outward from the back of the knife. Insert up to five blades backwards into the cartridge (it will be much easier to insert them as a single package rather than individually) until the latch actuates into their notch. Reinsert the cartridge into the knife housing and use the slider to load the active blade from the top of the stack by fully retracting it then sliding forward.
If you remove the slider you will note that the notch which selects and frees the active blade is an indentation of only a few micrometers - it is critical that when you use this knife you do not rely on the slider to retain the blade's position or you risk sliding the blade back into the cartridge or - much more dangerously - the blade may slide forward out of the housing and could even drop right out. Always make sure you use the locking knob after protruding the length of blade you wish to work with.
Reloading the cartridge is demonstrated in this video: