Jim,
By the question I suspect that you have greater need than the filler, which is not uncommon. There are several manufactuers that deal in the duplex fillers for a 25-5.
The first thing however I would suggest is do a forum search on duplex and research what has been well said in the forum already.
You should find quite a bit.
Though Ferralium is readily weldable, the welding 'window' for Ferralium is narrower than it is for the 2205's. And corrosion testing if imposed can be a problem, depending.