You probably won't get what you're looking for, no matter how long you wait.
I suggest that you just make a template, which you could do in a half hour. Just cut some mild curves on several large pieces of cardboard. Then piece them together in the boat against the bulkhead, and attach them to one another with tape. When you take it out, you can fair any un-fair segments on your template, and you're good to go. You can make a final template on another clean, large sheet of cardboard. It's not possible to replace the bulkhead with one piece; and it may even take three, with the last small one in between the beam in the forepeak and the bulkhead below the entryway in to that area (the owner's stateroom). It's just impossible to maneuver into position through the 'doorway' and aft of the beam.
When you put them in, use thickened epoxy in a caulking tube to close any gaps between the bulkhead, the hull, and the deck (so it doesn't try to move around as you sail through waves). Do the same between any separate pieces of bulkhead. Then make a cove with thickened epoxy at the bulkhead/hull joint, and then tape it with a couple of layers of 6-10 oz. glass tape. Use 2 or 3 layers also over any seams between bulkhead sections.
After having done this twice on my boat, in 1996, and then 10 years later, I can tell you that a few things are key to forestalling this problem:
1) keep the chainplates sealed at the deck.
2) If your boat leaks between the deck and the hull, correct that. It was kind of a big deal, but not so hard. Just take out all the fasteners, pry up the deck, scrape out the bedding compound, clean it up, and caulk it with a polyurethane caulk. I got about 50 gallons water in the boat over one winter before that! None now.
3) do what you can to seal the mast. I think spray foam in the mast track at deck level is good. Maybe some tape over the openings for lines on the sides during the off-season.
Then check it every now and then and make sure it's dry.
It's not so important that you use marine plywood. Just use some plywood and coat it with epoxy; 2 or 3 coats. If it's wet over a long period, marine plywood at 2 or 3 times the cost will do no better. It'll still rot.
It's been 16 years since I did it the second time, and the bulkhead is still just fine, but now in the hands of a new owner. The boat requires no bailing whatsoever.