Flange schematic

The problem with digital is the software/firmware to run it. Anymore its easier and probably cheaper to buy some kind of digital effects processor.

A short delay with delay time sweep (what flanging is) isn't all that hard to implement in DSP, if you have experience with assembly or C language.

Several DSP manufacturers (Analog Devices, TI etc.) have inexpensive DSP evaluation boards with assembly language editors/loaders which you can play around with if you're really interested in "rolling your own" DSP. They are kind of fun.

Other than that, you are looking at R&D expenses far beyond what a new effects processor would cost.

I have no idea if there would be enough of a market to pay for the expense of developing a board level DSP that could be added to an amp or housed in an external enclosure. Might have to think about that one...

Good luck
It is hard to believe that you couldn't find MN3101. I found it in the first shop I checked: http://sklep.avt.com.pl/go/_search/full_search.php?SEARCH_FORM=&search_query_words=MN3101
The site is only in Polish but you can see that they have both MN3101 and MN3007. They also sell "chorus" kit, which includes both of the ICs: http://sklep.avt.com.pl/p,pl,48309,...tarowy+-+zestaw+do+samodzielnego+montazu.html .
I can't believe that you couldn't find the ICs in the States.
You can also take a look at: http://www.tonepad.com/project.asp?id=26 . This is flanger build on MN3101 na MN3007.
If you want a digital version, you can take a look at: http://www.spinsemi.com/products.html . With this IC you can implement almost every delay-based effect, including flanger.