I don't believe aftermarket blades exist. When Fein was all there was, there wasn't a big reason for aftermarket manufacturers to get into the mix - just not enough tools out there to justify the tooling costs.
I read a recent comparison (I think in Fine Woodworking or Fine Home Building) of the new entrants into the "multi-master" tool corral.
The biggest disappointment? There were about 5 or 6 players (Craftsman, Dremel, Rockwell were some I can remember) - they all had different methods of attaching the blade...
The rub for the rest of us is that even though there's competition now, since most of the competitors use different attachment methods, and it's still an arguably microscopic market tool-wise, I'll bet aftermarket blade manufacturers will stay away in droves.
I think it's possible that Fein's attachment method is still under patent, as that feature was added to the tool a few years ago, if I remember correctly. Personally, I think it was Fein's attempt to get the overall patent extended.
I've googled until my fingers are numb and I can't turn up that article. What I do remember from it was Fein still rules the roost - more attachments, better design, more robust, etc. However, there were other tools that cost far less than the Fein that will likely work just fine for the "average joe".
Most of the articles I did find referred to the "proprietary" attachment method for the blades - which means no aftermarket...
I would like to think that possibly competition will drive the price down, but Fein has a HUGE following in the industrial crowd that will likely allow the prices to stay where they are - similar to Festool.
Needless to say, that blade was quickly returned to Woodcrafter. I was surprised at the variance in price for the same blade. As with everything, buyer beware...