Almost any 4x5" sheet film holders will fit your camera, all are pretty much the same in that they all hold a sheet of film, some however are slightly better to use than others.
In Way beyond Monochrome by Ralph Lambrecht and Chris Woodhouse, pages 108 - 110 there is a brief but excellent description of how to check for critical focusing with your film holder and your ground glass using a simple steel rule, toothpick and bull dog clip. It is also in their second edition but on pages 146 - 147 with the same pictures and probably the same text.
I myself have picked up many and various 4x5" film holders and find all work well, but some are just nicer to work with.
The best and nicest I have to work with are a couple of Toyo units, one is pictured.
The various Lisco units I have are all good, but I do find that the easiest ones to work with and with that have the least possibility of making errors with, are their MarkII version. This is the one with the elongated top on their slides. Not only are these easier to pull in and push in with thick gloves on, they also require the pushing of the little white button (by hand) to remove the dark slide. This little button, if not pushed in, will not allow the dark slide to be pulled out. When you insert one of these film holders into your camera back, unless the holder is correctly inserted, that little white button is not pushed in and you cannot pull the slide out.
This may not sound like a big deal, but every now and then it is quite possible to insert a film holder either not quite all the way in, or, depending upon the actual construction of your camera back, you can push a little too far. This doesn't sound like a big deal, but, if the film holder is not seated correctly, when you pull the dark slide there is an extremely good chance of getting a light leak between the film holder and the camera back. These film holders do have a slight drawback, they physically take more room than the other film holders I have. Not often an issue, but if I am travelling super tight, space wise, I leave these holders home.
The other Lisco units are great with the metal topped ones being the oldest I know of, but still work very well.
Things to watch out for are the little bent metal tabs missing, these are required to hold the dark slides in. The tape that acts as a hinge for the bottom flap shouldn't have any cracks in it, otherwise it needs to be replaced. I am holding a flap back, you can see that there are no breaks in this hinge.
Having a bent or kinked dark slide can be disastrous, I have a kink on a Toyo dark slide after I dropped the loaded holder onto the point of a rock. The resultant kink pulled the slide in and so far I haven't been able to eliminate that kink by using a ball pean hammer on an anvil.
Mick.