Italian railways are fascinating. Some of it is very modern, other parts less so. 2-6-0 625.100 was still listed as normal FS stock, as opposed to historic, until only a few years ago. The last steam workings were in the mid 80s. Locos like E626 electrics were virtually unchanged in 80 years. Yet they have hundreds of miles of high speed lines now, seemingly all in tunnels! The slate grey livery appeared on coaching stock in the late 60s, yet was still around on some vehicles this century, so there's a lot of overlap with some models.
I get a lot of my stuff from eBay, or Tecnomodel. My aunt lives in Livorno, so visits there are combined with a trip to the model shop as well. Amazon occasionally have a few Rivarossi bits for sale. I picked up a 744 2-8-0 a few weeks ago for a lot less than the RRP. At one point they had another version for about £105, instead of £178.
There are a few wagon kits available from Duegi Editrice that are good value. They need the wheels changing, which is a bit of a hassle as they're continental length 24.5mm axles, rather than the usual 26mm ones, but there are a few sources. DE also publish a lot of very good books and magazines. Not cheap, but some of the photos are stunning and full of detail.
www.duegieditricestore.it
When I finally get round to finishing off my shed, I'll be building an Italian layout. About 19' x 7', so a decent size! I've already got far too much stock for it as well, but keep buying bits!