I've just opened a shop in the Roman Market Macellum. All my current Samian ware, plus Celtic items are there. If you've not been to Roma before, it's a Roman sim selling Roman period goods plus Gladiator games and a themed area for homes.
I'm just up the stairs in the Market, near other traders selling Roman household furniture, clothing etc.
I think I put 44 Roman themed items there, so if you're after plain red Samian ware from the Iron Age Roman periods, you know where to go now.
I'm at Roma Suburba, 7, 81, 29
I haven't had time to put a shop sign up yet, so just look for the red pottery.