You can find it now in some supermarkets or at least gourmet markets.
You can also substitute a good sour cream in recipes.
Creme Fraiche - a matured cream in which natural acids have fermented and with time will thicken and takes on a slight nutty flavour with a slight tang
A pasteurised cream will not develop in the same way, so you do need to use fresh cows cream to make creme fraiche, unless you have access to a particular culture to produce a similar result. There is some produced commercially, it will keep for up to 2 weeks and will not curdle on cooking. A substitute is to add 1 tblsp plain full fat yoghurt to 150ml cream with a fat content of at least 30% in a bowl in warm water (bain marie) to heat slightly to activate the enzymes. Remove it from the water, cover and place in a warm spot. It takes about 12 - 36 hours. Chill before using - it will thicken further. Add sugar (brown?) or honey to sweeten. To whip 1/2 cream, 1/2 finely crushed ice and beat until thick. Mix it with prepared horseradish or mustard with finely chopped spring onion to serve with meat; mix with beetroot and orange rind in soup; in mashed potato; spread over chicken or fish before grilling, use in salads - a combination of mayo and creme fraiche, in scrambled eggs or an omelet; pasta sauces; stir through lemon cheese or custard for a dessert sauce; mix with banana, coconut, lemon and mint as a samba with curries; cucumber, onion and basil.
sometimes it also spelled creme fraise