You really need to keep the front and rear lens elements the correct distance apart from each other or they won’t perform properly.
I quickly searched “graflex top hat lens board” and found a listing on etsy that makes something like what you’re looking for but I don’t know if they make one that is compatible with your camera. You would have to measure your lens board and shutter to make sure.
If that doesn’t work there are places online that make custom lens boards. There are several but the only one I can think of is s. k. grimes. Maybe one of them will make you something.
If neither of those works you could talk to your nearest camera repair shop. Many of them have machining setups that would allow them to make what you need.
If not a camera shop then a machine shop could also do it.