I just received the Graphtec blade holder and Graphtec blades for the Silhouette. So far my results have been successful. I cut on 24# paper (which is usually harder than thicker paper) with great results. I'll keep you updated on my results as I cut with this blade and holder.
But if you would like an OEM blade, they have them at Archiver's and I have a 30% coupon for you here:
Lettering Delights has also released a new Intricate Gift Box Collection