Hi and welcome to the forum, Ive been coming here for all my info needs and to get a chance to talk to good people.
As mentioned
www.tzd.com is very reliable.
On ebay, as mentioned stay AWAY from Bullseye, he will rape you to tears.
http://www.japangamestock.com/ Is also excellent on a few but not all items.
I believe these coupon codes still work for cheaper shipping. Enter it in the coupon area.
TEAMFREMONT1000 for the 1,000 Yen discount
TEAMFREMONT500 for the 500 Yen discount.
You will probably need a Turbo Tap, find it NEW and Cheaper than TZD here
http://www.gameexpress.com/product_detail.cfm?UPC=092218007841and if you should get a Turbo Duo you can get controllers here (they wont work on your TG-16 without a converter cable, which D-lite can make for you.
http://www.gameexpress.com/product_detail.cfm?UPC=092218000026Forget the 2.0 card and go straight to the Arcade card PRO, even if you get a Duo later it will still work.
If you do get a duo, stay away from the regular model, get the DUO-R or DUO-RX instead.
Last but not least, as mentioned above GET IT MODDED by D-Lite I met him in person he is one of the best human beings on earth. He really cares about keeping our beloved Turbo/Engine alive. I am completely happy with my Duo-R that he sold me with all the bells and whisles.
Also go through all the previous threads, there are A LOT of great subjects to read about.
And ask questions! Even if it has been answered a million times, no one will flame you here. Everyone is cool.
Good luck, Long live the Turbo/Engine!