Sol,(posted 8641 days ago)There are only five B&W films available (that I am aware of) in 220 format. They are PXP, TXP, FP4, HP5 and Delta 400. I think you are better off using either of the ASA 125 films rather than pulling one of the ASA 400 films.
Lately, I have been experimenting with PXP format and developing in Rodinal 1:100 mixed with a 10% sodium sulfite solution. The largest I print is 16x20 (from 6x7 negs) and have been getting excellent results in terms of grain, accutance and tonal range (I think my enlarger lens has been holding back some of the sharpness).
If you want to go through the effort, I suppose you could re-spool your favorite 120 film onto a spool with a 220-length leader and trailer taped to the ends. You could advance through the remainder of the shots when you get to the end of the roll. Also I have seen Panatomic X (can we have a moment of silence for Panatomic X) being sold on ebay in 4 inch rolls. If you have a tool (and the desire) to cut down to 220 size, this may be your best alternative.
I have heard of Kodak making special orders, but you have to make it worth their while to make the production run (i.e. you have to order many thousands of dollars worth of whatever it is you want) and you have to be willing to wait for them to get around to your order as well.
Have you compared the results of the "super fine grained" films shot with your 120 back to the results of the traditional 220 films shot with your vacuum back? You may find that when all the variables play out there may be no discernable difference between your final prints
Best of luck, ~james