Welcome.
The best place to find a Supra is probably this forum, be extremely careful of certain stealerships that sell these cars as there are some real cowboys about. JM Imports is a safe bet and an authorised forum trader who could source and import a fresh Supra if you have the £££'s - http://www.mkivsupra.net/vbb/showthread.php?53679-Jm-Imports
There is loads of information on here, just have a good search.
For starters read this - http://www.mkivsupra.net/vbb/showthread.php?59334-Supra-Guide-and-Model-Differences-Chart and this http://www.mkivsupra.net/vbb/showthread.php?67644-What-to-check-when-buying-a-Supra.
If you find a car you like, post up on here with as much information as possible including any links to the car(s) in question and members will chip in with sound advice and help you out as best they can.
Steer clear of silly sized wheels and bodykits as bodykits can be used to hide all sorts of nasty things. You want a car with a good service history with receipts to back up any work and you need to look underneath these cars as they are getting old and British winters aren't kind to them.
Have fun