There are rear shock absorbers for sale on the Czech auktion Aukro.cz (similar eBay). The price seems be very good (13,72 € for each, a pair is available). Have you any experiences with the Cofap products quality?
http://www.aukro.cz/item1174342486_zadni_tlumic_renault_4_5_6.html#gallery
http://www.aukro.cz/item1174342486_zadni_tlumic_renault_4_5_6.html#gallery