I collect everything about Alain Prost and his son Nicolas since 30 years. Therefore I have a lot of connections and I'm willing to help you with addresses and more. I will also exchange items and photos and so on. Don't hesitate to contact me at firstname.lastname@example.org.
Nowadays you can find anything on auction platforms like eBay. Anyway, if you are looking for really special items like original helmets, driver suits and other rare items, you should contact specialized stores. It's important to know that original items of Alain Prost are often very expensive... Original worn Alain Prost helmets are normally sold for about 15'000 US-Dollars. Original driving suits are only a bit cheaper... Therefore, some people try to sell items which are not originals. I recommend asking the seller how he got the item and check the information with the producer (for example Sparco suits, Arai or Bell helmets)!
The same is true for autographs. If you have doubts about the authenticity of an Alain Prost autograph, you can always contact me and I will tell you if I think it's worth buying it.
If you want to buy or sell original Alain Prost helmets, suits, visors, nosecones, signatures, steering wheels, photos, prints and similar items, you can take a look at the following Websites:
If you are a collector of model cars, take a look at the following website:
For video tapes of F1 races with mostly German comments, you can contact Formel 1 Club Gattendorf. This Austrian Formula 1 Club sells video tapes of every race Alain participated in! If you speak German, you can become a member and get the tapes even cheaper! Of course, they also have lots of other memorabilia (like books) for sale...
Also take a look at my list of Alain Prost Books! You often find some of them on eBay.