There should be a car paint shop in your area which can make up the paint for you. All you need to do is quote the paint number 721. I was able to get some for my R4 quoting this 3 digit number.
I thought all car paint was now water based to meet environmental legislation. Might be wrong but I could not source cellulose for my R4 but got colour match in more modern paint.
Nu Agane are normally pretty good. Probably wasn't enough demand. Looks like cellulose is available via the internet (just googled). When you find someone who sells it tell them Renault 721 and also give the date of the car as colour numbers were ocasionally reused.
I think the rules at the moment are that solvent based car paints should only be used to restore historic vehicles and should not be used on run of the mill modern work. But I've not looked it up recently.