I had the same goal (collecting all GA Trades) but I've gotten so into it that now I'm also collecting single issues (for the moment the important ones or just shorter arcs, but yeah, I already see myself spending money on some old Detective Comics to get to the GA backup issues).
That said, you're missing some of the lesser known trades.
There is
-The Poison Tomorrow (a GA Bats crossover from the 80s or 90s by O'Neil)
->I'm actually not sure if it's a trade or just a one shot but in every case it's just one book (I've ordered it but haven't recieved it yet)
-Batman: The ring, the arrow and the bat
->this one has a misleading title! These are O'Neil stories (more or less canon, they kinda mix the Golden age stuff with later things and have their own take on certain established things, but continuity in GA is always a bit tricky) that show how GA met GL (so the first story is without Bats!) and later how GA met Bats.So you see, it's a GA trade.
-The Wonder Year-> it's Grell's take on the origin (so an older version of year one). I don't own it but I've read it. I don't like it too much. Compared to the rest of Grell's work it's somehow cheesy. But if you aim at a complete collection it should be included.
-Justice League: The rise and fall special-> other misleading title, this is a pure GA (first part) and Roy Harper (second part) story dealing with the aftermath of Cry For Justice.
-The 3rd Volume of Arrow is already available.
-Connor Hawke: Dragon's Blood (no idea if you intend to collect stories without Ollie Queen but this is the only Trade with Connor as main character (it's not from the time where he was the only GA it takes places somewhere after Ollie's resurrection).
-As a part of the Jack Kirby Omnibus series there should be a volume dedicated to GA (but I'm not sure how many of those stories the Showcase collection already has).
Maybe I've missed some. Don't know.
In any case, to understand GA and some of the concepts in some of the trades i recommend owning Identity Crisis (establishes his rivalery with both, Doctor Light and Deathstroke) and Cry For Justice (heavily leads into Rise and Fall and the storylines in Into The Woods and Salvation are also connected to the aftermath of that). I know, most people here hate those two stories but they're important to the character.
Oh! If you make an exception to the only trades rule get Green Arrow 96-101 from the 90's. That's the arc that ends with Ollie's death.
I hope this was of some help. Good luck with your collections folks!
these collection also feature green arrow
