Matt,
There are no upholstery kits available for these cars because the demand just isn't there. Seat covers will have to be custom made. If you are going the original route, SMS Auto Fabric may be able to supply the original materials. If you contact them with your data plate codes, they will send you samples of what they have that matches.
http://www.smsautofabrics.com
There is also a Original Auto Interiors, but I've never dealt with them. Looks like their website is down right now.
http://www.originalauto.com/
Paul