Nutley's 324ml Wide Mouth Clear Glass Jam Jar with Gingham Lid - Red (Pack of 12) https://www.amazon.co.uk/dp/B00EVVUHFM/ref=cm_sw_r_cp_api_i_ltIuFbRE9P7K6
They are these man, I guess they kind of are... they are wide mouth so I assumed they would
https://www.amazon.co.uk/dp/B00EVVUHFM/ref=cm_sw_r_cp_apa_i_qjZDCb9RAFYPV
12 for £18 though 24 works out cheaper per jar.
Technically they are a little bigger than half pint jars but they are close enough and most importantly the right shape.
Failing that get used to bonne mamam jam. More expensive than empty jars but you did get to eat jam.