Welcome to the wonderfully expensive world of '90s Imperials. Your radio is fairly common and came with many New Yorkers of the period. It took my sound guy a day to locate one for my '91. More at http://www.allpar.com/stereo/infinity-guide.html
Allpar has a few members who can help you with your overhead console problem, plus there's a special forum for Y bodies. Here's an example of a post on the topic. http://www.allpar.com/forums/index.php?showtopic=84966
Regarding your seats, bummer that they're stuck down because they become impossible to remove. Anything you can do to get power to the motor? How about removing the rails with the seats intact? Heavy as a you know what, though.
Happy motoring,
David
'91 K-Imperial driver 200,000 miles '66 LeBaron dual air and every option known to man