The blade on those secateurs looks very much worn: that's the reason why it seems so hard to keep closed. There isn't a whole lot of metal left.
This is absolutely normal for secateurs that get sharpened often.
You can get spare blades for most good quality secateurs (ARS, Felco, Fiskars etc). In Felco's case the design hasn't literally changed in over seventy years so even ancient ones can be fixed quickly and cheaply.
Yours look like an old Gardena design or a copy, and that could be a problem as Gardena blades have never been easy to find. Still an old Gardena or Husqvarna dealership (gardena is owned by Husky) may still have a few in stock.
