On Ebay I noticed a couple of kits put on offer by http://www.ebay.com/usr/maseratisource. I managed to get ahold of a set for an interesting price (US 165,-). Despite the shipping costs (US 69,-)and customs tax (€ 45,-) it was a very good deal in my opinion. Looking at Superformance.co.uk a similar set would cost about 3 times more. Although I'm not in need for these items I thought it would be handy to have them in my own stock for this price. I guess they are quite universal as they will fit at least on a 246 308 365 400 328 512 246 models.
Update: Typical, I now see on Ebay a Original Ferrari upper balljoint for sale at T. Rutlands, just for the records the part nr and price: