Try one of theese
82-88 BMW 5 Series E28 Style 128 Complete Body Kit by Erebuni Octane Motorsports
4 pc. kit include front bumper lip, pair of side skirts, and rear bumper lip. Fiberglass construction. Available for all models.
E12 E28 Body Kit by Custom Body Kits Conversions
And if all else fails, here is the google link to many sites that may have what you are looking for.
e28 body kit - Google Search