I know Better Imaging / Netprintz in Champaign, IL does E-6 processing and also does mail order. You might inquire there too. Their website is http://www.netprintz.net. Their phone number is (217) 352-0213 according to google+. Email the owner at lissaraybon@yahoo.com.

Just trying to help out with labs in the midwest that process E-6 and may be able to handle the E-6 film on polyester base. I know from experience that yes the Creve Coeur Camera lab can handle it. Not sure about the Better Imaging lab in Champaign but it doesn't hurt to ask.