There's a lady on Australian ebay that has been selling wool felt for ages, she has very good feedback and posts to the US. She has an off white colour, perhaps she can send you a small sample. Goodluck.
http://cgi.ebay.com.au/WOOL-FELT-CHOOSE … 588c0d91f4
last time i bought some woolfelt from them, one off-white, not thick, quite good to do with needle-sculpting.
see this link: http://www.probear.com/com/shop/pi14230 … egoryId=12
This is a link to a German woolfelt manufacturer, the 'Moll & Kühn’sche Filzfabrik': http://www.filzfabrik.de/eng/farbkollektionen.html (this is the page showing their so-called design felts).
On this website M&K mentions: We only supply trade customers. The following sales partners serve private customers and small quantities of less than 5 running metres : www.filzshop24.de and www.latroom.de so that would be something to bear in mind.
I hope this info is of some help
Hugs from Holland,