presumably they both have backs, so you don't need those.

You want fidelity style film holders -- can be bought new or used, you can find lots used for about $10 each. New can be had at Freestyle

Another option is the Grafmatic film holder -- it holds 6 sheets at once, costs $75 for good used at KEH.

All sheet film holders can be used with any kind of back that your camera has on it, spring or graflok. The crown should have a graflok on it, but no matter, they all use film holders.

I'll give you $5 for your spare body

if you go to you will find a massive data resource on these amazing and highly useful cameras.