http://www.schmiedmann.com is a large company selling BMW parts at competitive prices and they ship worldwide!
They already show a lot of E21 parts on their website and they can supply even more E21 parts, just email them your request. Further, you can search their website using the OEM part #. These part numbers can be found on http://www.realoem.com or http://www.bmwfans.info
Further, they supply a whole lot more parts for nearly all BMW's from the 1970's onwards!
And it gets better: if you order with them and supply your bmwe21.net userid in the comments field, you will receive a 10% discount!
Just use this format:
Have a look on their website now! http://www.schmiedmann.combmwe21.net userid=...