JJB Sports used to sell them but couldn't be sure if they still do. Elverys do them and so do Lifestyle I think. Argos have them on page 1189 of their current catalogue, they have a junior one cat # 010/7532 for €12.99 and a full size one cat # 072/2890 for €14.99. They are only available in the Extra stores so bear that in mind when looking.
ps I have no affiliation with the above mentioned companies, hubby plays American Football so have had to buy a few in the past