Thin and narrow strip of metal(preferably brass or steel, aluminium and copper could be too soft). The edges/frame of a sheet of photoetch comes to mind ...
Fine grade sandpaper, wider than the strip, fold and superglue the metal strip in the fold. Result: small sandpaper file with a slightly rounded edge.
If you get one of these (jeweler's saw):https://www.amazon.com/SE-81970SF-Adjustable-Jewelers-Professional/dp/B008CO8JZE
you can clamp the metal-sandpaper combo in the holders and use the sandpaper instead of a sawblade and avoid the super gluing.
One side of the spring coils is accessible without problems, the other side (inside the "arm") can be handled by threading the file-blade through the hole before clamping into the jeweler's saw.
Many years ago I bought "metal sandpaper", narrow strips of thin steel (0.2 mm or less) with a sandpaper structure on one surface. Clamped in the jeweler's saw it becomes a hybrid between a saw, a file and a sandpaper.
Holding it with four fingers in one hand is possible but requires a lot of dexterity and training.
One of these could also be used if the metal strip is long enough( fret saw or coping saw): https://www.amazon.com/Eclipse-70-FS1R-Handle-Coping-Thickness/dp/B01D0CHOZI/ref=sr_1_3?s=hi&ie=UTF8&qid=1502697932&sr=1-3&keywords=fret+saw
Both of these saw types are very useful in modelling.
With a fine blade for metal they are excellent for cutting difficult sprue attachments where side cutters or knife will not work due to tight space or danger of stressing the part so that it breaks (delicate track links for instance).
Cutting out large holes is also easy.