Congratulations and welcome. I own two Benelli Supersports (it's Supersport, not special sport). If you'll look at the top of the page, you'll see a sticky for parts suppliers-classics - that's where the parts suppliers are listed. Except for the seat cover, that is- I don't think you'll ever find that. Tank badges: I've seen both the plastic ones you have, and white vinyl logos. Both my Benellis had white vinyl and I had those ( and the "250 Supersport" tool box lid graphics that you're missing) made locally- you'll have to do the same.
You don't list any location- are you in the UK, or USA perhaps?