I have the K552N - and the last thing I'd describe the keycaps as, would be "sandy".
Do you have one of the RGB variants? If so, it's probably a different 'feel' for those, as they're manufactured to have the light shine through elements of the caps (I believe, from images at least - perhaps they're just coloured?).
As I understand it, Redragon use a pretty standard keycap for the switches in use, so you should be fine ordering any set that appear compatible from the likes of Aliexpress etc.