Hi:
You can use the standard Hasselbald V - Phase One cable that attaches to the flash sync on the lens and "double shoot"-- one to wake the back up and the next one within 3-5 seconds to take the actual exposure.
I was able to purchase additional ones from Calumet in the San Francisco Bay Area for about $20. I think the person I talked with was "Gene", but I would just ask for the "Professional Digital" guy. He'll know the cable.
I assume that you have a P25 with a Hasselbald mount. There are two adapter plates that are reasonably priced and "easy" to obtain-- one is by Horseman and the other by Linhof.
The Horseman does not fit the P-back. For some reason the cutout isn't compatible (with the P45). Any Graflock/4x5 to Hassie filmback adapter you will need to try the back on to make sure it fits.
The Linhof does correctly fit the P-series and fits most 4x5s that have a Graflok adapter. However, some 4x5 cameras don't have a "pure" Graflock spec'd area-- I found this on my Ebony and the Linhof adapter.
I would call Badger graphic and ask them which Graflok/view camera to Hasselblad film back adapters they carry--- they might let you try them on spec.
Expect to spend in the $300-$400 range for a new Graflock to Hassie filmback adapter.
The Phase One adapter is about $2000, allows stitching, etc. but is quite pricey. It is also a little bulky-- I was looking for something to backpack with.
Hope this gets you started. Don't hesitate to follow-up with me on this. I went through this journey last year. I found locating the Graflok/4x5 adapter that worked to be the most difficult.
Good luck!
Rich
NGOphotographer