Unfortunately, Fiat only sell that bush as part of an entire subframe. Believe me, you don't want to see the price!
Fortunately, some clever folk on here have found a workaround. It's possible to use the subframe bushes from another Fiat (which are sold separately), knock the old ones out and drop a new one in. Hurrah!
However, it's not quite that simple. The replacement bush (someone on ebay sells them for around £25 each - I'll try to find a link as it's not listed as a Multipla item) won't quite fit the subframe hole as-is. You'll have to find someone with a lathe and simple mandrel to turn the bush housing down by 1-2mm.
So, not as simple as it could be, but a lot cheaper than Fiat would have it.