Yes, you need to go to a "proper" post office and ask, although they do usually have them displayed somewhere behind glass or getting dusty on a shelf because they're not very good at advertising them
We lived in Limassol and had our own post office in the village we lived in at Ypsonas but the one at Polemidia not far from the General Hospital was our main office for 9yrs before we got the village one because we got classed as a suburb...
No prices here, but:
https://www.cypruspost.post/en/eidi-siskeuasias
Packaging Material
You may purchase packaging material at all Post Offices, suitable to satisfy every need, at very affordable prices. There are:
Carton boxes in 7 different sizes
Bubble envelopes in 4 different sizes
A’ Priority envelopes