You can find the tan slip covers with the Ferrari script on them on Ebay quite often....in fact there's a pair of them for auction right now. Just type "Ferrari 308" in the search field, and then choose "newly listed" and scroll down a page or two and you should see them. Starting bid was something like $9.00 or so. I have these on my 308 and they are easy to slip on and off. Should fit the 328's no problem. Hope this helps.
you can even find the original ones, with a bit of patience and luck (but they will cost you more). Sorry, I just realized this is a zombie thread...
I bought a set of the original tan denim versions on eBay and they are great, but I also picked up a pair of the more modern red satin covers that also work fine from Eurospares UK.