I have found a supplier of the excellent, fully synthetic TOTAL QUARTZ 9000 5W/40 oil for the Diesel Citroen C3s (without DPF/FAP).
It meets ACEA 2007 A3/B4 and is available in 5 litre containers (full change with some spare as you will need 4 or less litres):

Total Quartz Energy 9000 5W-40 Motor Oil - 5L at Amazon.co.uk
(for the Petrol C3, use this Total Quartz 7000 10W-40 Motor Oil - 5L (click here)
When changing the oil, also change the oil filter, find the correct filter for your engine here (euro car parts).
For the Citroen C3 1.6HDi with the Diesel particulate filter (FAP/DPF) a low SAPS oil is REQUIRED, have a look at:
TOTAL Quartz Ineo Long Life 5w30 Fully Synthetic Engine Oil. 5 Litre a suitable Total oil with a Low SAPS (Sulphated Ash, Phosphorus, Sulphur) rated at ACEA C3 and graded as 5W30.
If budget is tight, oil changes are frequent or fully synthetic not required and there is no DPF or FAP.
Then the Quartz 7000 10W/40 (semi synthetic) is also available. Not for use in a 16v HDi engine, but suitable for older 8v diesels and the petrols engines.

Available here: TOTAL Quartz 7000 10w40 Semi Synthetic Engine Oil. 5 Litre,often with free delivery
