I agree that it is not easy to find dongles with Widcomm stack, it looks like this one is becoming less popular.
Anycom has dongles using Widcomm only, but has discontinued their USB-250 and USB-200 dongles.
One option might be the fairly new Anycom USB-500, which you can bye at e.g. amazon.de.
Unfortunately also the widcomm dongles are more costly, the cheap ones mostly use the blue-soleil stack.
I´d love to see Franson to support the Blue-Soleil stack, but I´m afraid that won´t happen, as there has not been any BlueTools update for a long time.
Best regards - MacSass